use std::io;

use ed25519_dalek::Signer as _;
use p256::elliptic_curve::sec1::ToEncodedPoint;
use pkcs8::{DecodePrivateKey, DecodePublicKey, EncodePrivateKey, EncodePublicKey};
use rand::RngCore;
use rand::rngs::OsRng;
use rsa::{
    RsaPrivateKey, RsaPublicKey,
    hazmat::{rsa_decrypt_and_check as rsa_decrypt_raw, rsa_encrypt as rsa_encrypt_raw},
    traits::{PrivateKeyParts, PublicKeyParts},
};
use sha2::Digest as _;
use signature::Verifier;
use subtle::ConstantTimeEq as _;
use zeroize::{Zeroize, Zeroizing};

pub(crate) struct KeyPairDer {
    pub private: Zeroizing<Vec<u8>>,
    pub public: Vec<u8>,
    pub length: usize,
    pub exponent: Vec<u8>,
}

fn unsupported() -> io::Error {
    io::Error::other("Unsupported asymmetric crypto operation")
}

fn hash_bytes(name: &str, data: &[u8]) -> io::Result<Vec<u8>> {
    match name {
        "SHA-1" => Ok(sha1::Sha1::digest(data).to_vec()),
        "SHA-256" => Ok(sha2::Sha256::digest(data).to_vec()),
        "SHA-384" => Ok(sha2::Sha384::digest(data).to_vec()),
        "SHA-512" => Ok(sha2::Sha512::digest(data).to_vec()),
        _ => Err(unsupported()),
    }
}

pub(crate) fn generate(
    name: &str,
    length: usize,
    exponent: &[u8],
    curve: &str,
) -> io::Result<KeyPairDer> {
    let mut rng = OsRng;
    match name {
        "RSA-OAEP" | "RSA-PSS" | "RSASSA-PKCS1-V1_5" => {
            if !(512..=8192).contains(&length) || !length.is_multiple_of(8) || exponent.is_empty() {
                return Err(io::Error::other("Invalid RSA key parameters"));
            }
            let exp = rsa::BigUint::from_bytes_be(exponent);
            let exponent_bytes = exp.to_bytes_be();
            if exp < rsa::BigUint::from(3u8)
                || exponent_bytes.last().is_none_or(|byte| byte % 2 == 0)
            {
                return Err(io::Error::other("Invalid RSA public exponent"));
            }
            let private =
                RsaPrivateKey::new_with_exp(&mut rng, length, &exp).map_err(io::Error::other)?;
            let public = RsaPublicKey::from(&private);
            let private_der = private.to_pkcs8_der().map_err(io::Error::other)?;
            let public_der = public.to_public_key_der().map_err(io::Error::other)?;
            Ok(KeyPairDer {
                private: Zeroizing::new(private_der.as_bytes().to_vec()),
                public: public_der.as_bytes().to_vec(),
                length,
                exponent: exp.to_bytes_be(),
            })
        }
        "ECDSA" | "ECDH" => match curve {
            "P-256" => {
                let private = p256::SecretKey::random(&mut rng);
                let public = private.public_key();
                Ok(KeyPairDer {
                    private: Zeroizing::new(
                        private
                            .to_pkcs8_der()
                            .map_err(io::Error::other)?
                            .as_bytes()
                            .to_vec(),
                    ),
                    public: public
                        .to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 256,
                    exponent: Vec::new(),
                })
            }
            "P-384" => {
                let private = p384::SecretKey::random(&mut rng);
                let public = private.public_key();
                Ok(KeyPairDer {
                    private: Zeroizing::new(
                        private
                            .to_pkcs8_der()
                            .map_err(io::Error::other)?
                            .as_bytes()
                            .to_vec(),
                    ),
                    public: public
                        .to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 384,
                    exponent: Vec::new(),
                })
            }
            "P-521" => {
                let private = p521::SecretKey::random(&mut rng);
                let public = private.public_key();
                Ok(KeyPairDer {
                    private: Zeroizing::new(
                        private
                            .to_pkcs8_der()
                            .map_err(io::Error::other)?
                            .as_bytes()
                            .to_vec(),
                    ),
                    public: public
                        .to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 521,
                    exponent: Vec::new(),
                })
            }
            _ => Err(unsupported()),
        },
        "ED25519" => {
            let private = ed25519_dalek::SigningKey::generate(&mut rng);
            let public = private.verifying_key();
            Ok(KeyPairDer {
                private: Zeroizing::new(
                    private
                        .to_pkcs8_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                ),
                public: public
                    .to_public_key_der()
                    .map_err(io::Error::other)?
                    .as_bytes()
                    .to_vec(),
                length: 256,
                exponent: Vec::new(),
            })
        }
        "X25519" => {
            let mut secret = [0u8; 32];
            rng.fill_bytes(&mut secret);
            let private = x25519_dalek::StaticSecret::from(secret);
            secret.zeroize();
            let public = x25519_dalek::PublicKey::from(&private);
            let private_der = Zeroizing::new(private.to_bytes().to_vec());
            Ok(KeyPairDer {
                private: private_der,
                public: public.to_bytes().to_vec(),
                length: 256,
                exponent: Vec::new(),
            })
        }
        _ => Err(unsupported()),
    }
}

pub(crate) struct ImportedKey {
    pub bytes: Vec<u8>,
    pub length: usize,
    pub exponent: Vec<u8>,
    pub curve: String,
}

fn x25519_der(private: bool, key: &[u8]) -> io::Result<Vec<u8>> {
    let prefix: &[u8] = if private {
        &[
            0x30, 0x2e, 0x02, 0x01, 0x00, 0x30, 0x05, 0x06, 0x03, 0x2b, 0x65, 0x6e, 0x04, 0x22,
            0x04, 0x20,
        ]
    } else {
        &[
            0x30, 0x2a, 0x30, 0x05, 0x06, 0x03, 0x2b, 0x65, 0x6e, 0x03, 0x21, 0x00,
        ]
    };
    if key.len() != 32 {
        return Err(unsupported());
    }
    let mut der = prefix.to_vec();
    der.extend_from_slice(key);
    Ok(der)
}

fn x25519_from_der(private: bool, der: &[u8]) -> io::Result<Vec<u8>> {
    let prefix: &[u8] = if private {
        &[
            0x30, 0x2e, 0x02, 0x01, 0x00, 0x30, 0x05, 0x06, 0x03, 0x2b, 0x65, 0x6e, 0x04, 0x22,
            0x04, 0x20,
        ]
    } else {
        &[
            0x30, 0x2a, 0x30, 0x05, 0x06, 0x03, 0x2b, 0x65, 0x6e, 0x03, 0x21, 0x00,
        ]
    };
    if der.len() != prefix.len() + 32 || !der.starts_with(prefix) {
        return Err(unsupported());
    }
    Ok(der[prefix.len()..].to_vec())
}

fn ec_public_sec1(der: &[u8]) -> io::Result<Vec<u8>> {
    let info = pkcs8::spki::SubjectPublicKeyInfoRef::try_from(der).map_err(io::Error::other)?;
    info.subject_public_key
        .as_bytes()
        .map(ToOwned::to_owned)
        .ok_or_else(unsupported)
}

pub(crate) fn import_key(
    format: &str,
    data: &[u8],
    name: &str,
    curve: &str,
) -> io::Result<ImportedKey> {
    let private = format == "pkcs8";
    if format == "raw" && private {
        return Err(unsupported());
    }
    if !matches!(format, "raw" | "spki" | "pkcs8") {
        return Err(unsupported());
    }
    match name {
        "RSA-OAEP" | "RSA-PSS" | "RSASSA-PKCS1-V1_5" => {
            let (bytes, length, exponent) = if private {
                let key = RsaPrivateKey::from_pkcs8_der(data).map_err(io::Error::other)?;
                if !(512..=8192).contains(&key.n().bits()) {
                    return Err(io::Error::other("Invalid RSA modulus size"));
                }
                let bytes = key
                    .to_pkcs8_der()
                    .map_err(io::Error::other)?
                    .as_bytes()
                    .to_vec();
                (bytes, key.n().bits(), key.e().to_bytes_be())
            } else {
                let key = RsaPublicKey::from_public_key_der(data).map_err(io::Error::other)?;
                if !(512..=8192).contains(&key.n().bits()) {
                    return Err(io::Error::other("Invalid RSA modulus size"));
                }
                let bytes = key
                    .to_public_key_der()
                    .map_err(io::Error::other)?
                    .as_bytes()
                    .to_vec();
                (bytes, key.n().bits(), key.e().to_bytes_be())
            };
            Ok(ImportedKey {
                bytes,
                length,
                exponent,
                curve: String::new(),
            })
        }
        "ECDSA" | "ECDH" => match (curve, format) {
            ("P-256", "raw") => {
                let key = p256::PublicKey::from_sec1_bytes(data).map_err(io::Error::other)?;
                Ok(ImportedKey {
                    bytes: key
                        .to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 256,
                    exponent: Vec::new(),
                    curve: curve.into(),
                })
            }
            ("P-256", "pkcs8") => {
                let key = p256::SecretKey::from_pkcs8_der(data).map_err(io::Error::other)?;
                Ok(ImportedKey {
                    bytes: key
                        .to_pkcs8_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 256,
                    exponent: Vec::new(),
                    curve: curve.into(),
                })
            }
            ("P-256", "spki") => {
                let key = p256::PublicKey::from_public_key_der(data).map_err(io::Error::other)?;
                Ok(ImportedKey {
                    bytes: key
                        .to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 256,
                    exponent: Vec::new(),
                    curve: curve.into(),
                })
            }
            ("P-384", "raw") => {
                let key = p384::PublicKey::from_sec1_bytes(data).map_err(io::Error::other)?;
                Ok(ImportedKey {
                    bytes: key
                        .to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 384,
                    exponent: Vec::new(),
                    curve: curve.into(),
                })
            }
            ("P-384", "pkcs8") => {
                let key = p384::SecretKey::from_pkcs8_der(data).map_err(io::Error::other)?;
                Ok(ImportedKey {
                    bytes: key
                        .to_pkcs8_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 384,
                    exponent: Vec::new(),
                    curve: curve.into(),
                })
            }
            ("P-384", "spki") => {
                let key = p384::PublicKey::from_public_key_der(data).map_err(io::Error::other)?;
                Ok(ImportedKey {
                    bytes: key
                        .to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 384,
                    exponent: Vec::new(),
                    curve: curve.into(),
                })
            }
            ("P-521", "raw") => {
                let key = p521::PublicKey::from_sec1_bytes(data).map_err(io::Error::other)?;
                Ok(ImportedKey {
                    bytes: key
                        .to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 521,
                    exponent: Vec::new(),
                    curve: curve.into(),
                })
            }
            ("P-521", "pkcs8") => {
                let key = p521::SecretKey::from_pkcs8_der(data).map_err(io::Error::other)?;
                Ok(ImportedKey {
                    bytes: key
                        .to_pkcs8_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 521,
                    exponent: Vec::new(),
                    curve: curve.into(),
                })
            }
            ("P-521", "spki") => {
                let sec1 = ec_public_sec1(data)?;
                let key = p521::PublicKey::from_sec1_bytes(&sec1).map_err(io::Error::other)?;
                Ok(ImportedKey {
                    bytes: key
                        .to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 521,
                    exponent: Vec::new(),
                    curve: curve.into(),
                })
            }
            _ => Err(unsupported()),
        },
        "ED25519" => match format {
            "raw" => {
                let public: [u8; 32] = data
                    .try_into()
                    .map_err(|_| io::Error::other("Invalid key length"))?;
                let key =
                    ed25519_dalek::VerifyingKey::from_bytes(&public).map_err(io::Error::other)?;
                Ok(ImportedKey {
                    bytes: key
                        .to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 256,
                    exponent: Vec::new(),
                    curve: String::new(),
                })
            }
            "spki" => {
                let key = ed25519_dalek::VerifyingKey::from_public_key_der(data)
                    .map_err(io::Error::other)?;
                Ok(ImportedKey {
                    bytes: key
                        .to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 256,
                    exponent: Vec::new(),
                    curve: String::new(),
                })
            }
            "pkcs8" => {
                let key =
                    ed25519_dalek::SigningKey::from_pkcs8_der(data).map_err(io::Error::other)?;
                Ok(ImportedKey {
                    bytes: key
                        .to_pkcs8_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length: 256,
                    exponent: Vec::new(),
                    curve: String::new(),
                })
            }
            _ => Err(unsupported()),
        },
        "X25519" => {
            let bytes = match format {
                "raw" | "spki" if !private => {
                    if format == "raw" {
                        data.to_vec()
                    } else {
                        x25519_from_der(false, data)?
                    }
                }
                "pkcs8" if private => x25519_from_der(true, data)?,
                _ => return Err(unsupported()),
            };
            if bytes.len() != 32 {
                return Err(unsupported());
            }
            Ok(ImportedKey {
                bytes,
                length: 256,
                exponent: Vec::new(),
                curve: String::new(),
            })
        }
        _ => Err(unsupported()),
    }
}

pub(crate) fn export_key(
    format: &str,
    data: &[u8],
    name: &str,
    key_type: &str,
    curve: &str,
) -> io::Result<Vec<u8>> {
    if (format == "raw" && key_type == "private")
        || (format == "pkcs8" && key_type != "private")
        || (format == "spki" && key_type != "public")
    {
        return Err(io::Error::other(
            "InvalidAccessError: key type is incompatible with key format",
        ));
    }
    match (format, name, key_type) {
        (
            "pkcs8",
            "RSA-OAEP" | "RSA-PSS" | "RSASSA-PKCS1-V1_5" | "ECDSA" | "ECDH" | "ED25519",
            "private",
        ) => Ok(data.to_vec()),
        (
            "spki",
            "RSA-OAEP" | "RSA-PSS" | "RSASSA-PKCS1-V1_5" | "ECDSA" | "ECDH" | "ED25519",
            "public",
        ) => Ok(data.to_vec()),
        ("raw", "ECDSA" | "ECDH", "public") => match curve {
            "P-256" => Ok(p256::PublicKey::from_public_key_der(data)
                .map_err(io::Error::other)?
                .to_encoded_point(false)
                .as_bytes()
                .to_vec()),
            "P-384" => Ok(p384::PublicKey::from_public_key_der(data)
                .map_err(io::Error::other)?
                .to_encoded_point(false)
                .as_bytes()
                .to_vec()),
            "P-521" => Ok(ec_public_sec1(data)?),
            _ => Err(unsupported()),
        },
        ("raw", "ED25519", "public") => Ok(ed25519_dalek::VerifyingKey::from_public_key_der(data)
            .map_err(io::Error::other)?
            .to_bytes()
            .to_vec()),
        ("raw", "X25519", "public") => Ok(data.to_vec()),
        ("spki", "X25519", "public") => x25519_der(false, data),
        ("pkcs8", "X25519", "private") => x25519_der(true, data),
        _ => Err(unsupported()),
    }
}

fn jwk_bytes(value: &serde_json::Value, field: &str) -> io::Result<Vec<u8>> {
    use base64::Engine;
    use base64::engine::general_purpose::URL_SAFE_NO_PAD;
    let encoded = value
        .get(field)
        .and_then(serde_json::Value::as_str)
        .ok_or_else(|| io::Error::other("JWK field is missing"))?;
    URL_SAFE_NO_PAD.decode(encoded).map_err(io::Error::other)
}

fn b64(bytes: &[u8]) -> String {
    use base64::Engine;
    use base64::engine::general_purpose::URL_SAFE_NO_PAD;
    URL_SAFE_NO_PAD.encode(bytes)
}

pub(crate) fn import_jwk(
    jwk: &serde_json::Value,
    name: &str,
    hash: &str,
    curve: &str,
) -> io::Result<(ImportedKey, String)> {
    match name {
        "RSA-OAEP" | "RSA-PSS" | "RSASSA-PKCS1-V1_5" => {
            if jwk.get("kty").and_then(serde_json::Value::as_str) != Some("RSA") {
                return Err(io::Error::other("JWK kty does not match RSA"));
            }
            if jwk.get("oth").is_some() {
                return Err(io::Error::other("Multiprime RSA JWKs are unsupported"));
            }
            let n_bytes = jwk_bytes(jwk, "n")?;
            let e_bytes = jwk_bytes(jwk, "e")?;
            if n_bytes.is_empty() || e_bytes.is_empty() || n_bytes[0] == 0 || e_bytes[0] == 0 {
                return Err(io::Error::other("Invalid RSA JWK integer encoding"));
            }
            let n = rsa::BigUint::from_bytes_be(&n_bytes);
            if n.bits() < 512 || n.bits() > 8192 {
                return Err(io::Error::other("Invalid RSA modulus size"));
            }
            let e = rsa::BigUint::from_bytes_be(&e_bytes);
            let private = jwk.get("d").is_some();
            let (bytes, length) = if private {
                let d = rsa::BigUint::from_bytes_be(&jwk_bytes(jwk, "d")?);
                let p = rsa::BigUint::from_bytes_be(&jwk_bytes(jwk, "p")?);
                let q = rsa::BigUint::from_bytes_be(&jwk_bytes(jwk, "q")?);
                let dp = rsa::BigUint::from_bytes_be(&jwk_bytes(jwk, "dp")?);
                let dq = rsa::BigUint::from_bytes_be(&jwk_bytes(jwk, "dq")?);
                let qi = rsa::BigUint::from_bytes_be(&jwk_bytes(jwk, "qi")?);
                let mut key = RsaPrivateKey::from_components(n, e, d, vec![p, q])
                    .map_err(io::Error::other)?;
                key.precompute().map_err(io::Error::other)?;
                key.validate().map_err(io::Error::other)?;
                if key.dp() != Some(&dp)
                    || key.dq() != Some(&dq)
                    || key.qinv().and_then(|v| v.to_biguint()).as_ref() != Some(&qi)
                {
                    return Err(io::Error::other("JWK RSA CRT parameters do not match"));
                }
                let length = key.n().bits();
                (
                    key.to_pkcs8_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length,
                )
            } else {
                let key = RsaPublicKey::new(n, e).map_err(io::Error::other)?;
                let length = key.n().bits();
                (
                    key.to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    length,
                )
            };
            let expected_alg = match name {
                "RSA-OAEP" => {
                    if hash == "SHA-1" {
                        "RSA-OAEP".to_owned()
                    } else {
                        format!("RSA-OAEP-{}", &hash[4..])
                    }
                }
                "RSA-PSS" => format!("PS{}", &hash[4..]),
                _ => format!("RS{}", &hash[4..]),
            };
            if let Some(alg) = jwk.get("alg")
                && alg.as_str() != Some(expected_alg.as_str())
            {
                return Err(io::Error::other("JWK alg does not match RSA hash"));
            }
            Ok((
                ImportedKey {
                    bytes,
                    length,
                    exponent: e_bytes,
                    curve: String::new(),
                },
                if private { "private" } else { "public" }.into(),
            ))
        }
        "ECDSA" | "ECDH" => {
            if jwk.get("kty").and_then(serde_json::Value::as_str) != Some("EC") {
                return Err(io::Error::other("JWK kty does not match EC"));
            }
            let expected_curve = match curve {
                "P-256" => "P-256",
                "P-384" => "P-384",
                "P-521" => "P-521",
                _ => return Err(unsupported()),
            };
            if jwk.get("crv").and_then(serde_json::Value::as_str) != Some(expected_curve) {
                return Err(io::Error::other("JWK curve does not match"));
            }
            let x = jwk_bytes(jwk, "x")?;
            let y = jwk_bytes(jwk, "y")?;
            let width = match curve {
                "P-256" => 32,
                "P-384" => 48,
                "P-521" => 66,
                _ => return Err(unsupported()),
            };
            if x.len() != width || y.len() != width {
                return Err(io::Error::other("Invalid EC JWK coordinate length"));
            }
            let private = jwk.get("d").is_some();
            if private && jwk_bytes(jwk, "d")?.len() != width {
                return Err(io::Error::other("Invalid EC JWK private key length"));
            }
            let mut point = Vec::with_capacity(1 + x.len() + y.len());
            point.push(4);
            point.extend_from_slice(&x);
            point.extend_from_slice(&y);
            let (bytes, length) = match (curve, private) {
                ("P-256", true) => {
                    let key = p256::SecretKey::from_slice(&jwk_bytes(jwk, "d")?)
                        .map_err(io::Error::other)?;
                    if key.public_key().to_encoded_point(false).as_bytes() != point {
                        return Err(io::Error::other(
                            "JWK EC public and private values disagree",
                        ));
                    }
                    (
                        key.to_pkcs8_der()
                            .map_err(io::Error::other)?
                            .as_bytes()
                            .to_vec(),
                        256,
                    )
                }
                ("P-256", false) => (
                    p256::PublicKey::from_sec1_bytes(&point)
                        .map_err(io::Error::other)?
                        .to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    256,
                ),
                ("P-384", true) => {
                    let key = p384::SecretKey::from_slice(&jwk_bytes(jwk, "d")?)
                        .map_err(io::Error::other)?;
                    if key.public_key().to_encoded_point(false).as_bytes() != point {
                        return Err(io::Error::other(
                            "JWK EC public and private values disagree",
                        ));
                    }
                    (
                        key.to_pkcs8_der()
                            .map_err(io::Error::other)?
                            .as_bytes()
                            .to_vec(),
                        384,
                    )
                }
                ("P-384", false) => (
                    p384::PublicKey::from_sec1_bytes(&point)
                        .map_err(io::Error::other)?
                        .to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    384,
                ),
                ("P-521", true) => {
                    let key = p521::SecretKey::from_slice(&jwk_bytes(jwk, "d")?)
                        .map_err(io::Error::other)?;
                    if key.public_key().to_encoded_point(false).as_bytes() != point {
                        return Err(io::Error::other(
                            "JWK EC public and private values disagree",
                        ));
                    }
                    (
                        key.to_pkcs8_der()
                            .map_err(io::Error::other)?
                            .as_bytes()
                            .to_vec(),
                        521,
                    )
                }
                ("P-521", false) => (
                    p521::PublicKey::from_sec1_bytes(&point)
                        .map_err(io::Error::other)?
                        .to_public_key_der()
                        .map_err(io::Error::other)?
                        .as_bytes()
                        .to_vec(),
                    521,
                ),
                _ => return Err(unsupported()),
            };
            Ok((
                ImportedKey {
                    bytes,
                    length,
                    exponent: Vec::new(),
                    curve: curve.into(),
                },
                if private { "private" } else { "public" }.into(),
            ))
        }
        "ED25519" => {
            if jwk.get("kty").and_then(serde_json::Value::as_str) != Some("OKP")
                || jwk.get("crv").and_then(serde_json::Value::as_str) != Some("Ed25519")
            {
                return Err(io::Error::other("JWK is not Ed25519"));
            }
            let x: [u8; 32] = jwk_bytes(jwk, "x")?
                .try_into()
                .map_err(|_| io::Error::other("Invalid key length"))?;
            let private = jwk.get("d").is_some();
            let bytes = if private {
                let d: [u8; 32] = jwk_bytes(jwk, "d")?
                    .try_into()
                    .map_err(|_| io::Error::other("Invalid key length"))?;
                let key = ed25519_dalek::SigningKey::from_bytes(&d);
                if key.verifying_key().to_bytes() != x {
                    return Err(io::Error::other("JWK public and private values disagree"));
                }
                key.to_pkcs8_der()
                    .map_err(io::Error::other)?
                    .as_bytes()
                    .to_vec()
            } else {
                ed25519_dalek::VerifyingKey::from_bytes(&x)
                    .map_err(io::Error::other)?
                    .to_public_key_der()
                    .map_err(io::Error::other)?
                    .as_bytes()
                    .to_vec()
            };
            Ok((
                ImportedKey {
                    bytes,
                    length: 256,
                    exponent: Vec::new(),
                    curve: String::new(),
                },
                if private { "private" } else { "public" }.into(),
            ))
        }
        "X25519" => {
            if jwk.get("kty").and_then(serde_json::Value::as_str) != Some("OKP")
                || jwk.get("crv").and_then(serde_json::Value::as_str) != Some("X25519")
            {
                return Err(io::Error::other("JWK is not X25519"));
            }
            let x: [u8; 32] = jwk_bytes(jwk, "x")?
                .try_into()
                .map_err(|_| io::Error::other("Invalid key length"))?;
            let private = jwk.get("d").is_some();
            let bytes = if private {
                let d: [u8; 32] = jwk_bytes(jwk, "d")?
                    .try_into()
                    .map_err(|_| io::Error::other("Invalid key length"))?;
                let secret = x25519_dalek::StaticSecret::from(d);
                if x25519_dalek::PublicKey::from(&secret).to_bytes() != x {
                    return Err(io::Error::other("JWK public and private values disagree"));
                }
                d.to_vec()
            } else {
                x.to_vec()
            };
            Ok((
                ImportedKey {
                    bytes,
                    length: 256,
                    exponent: Vec::new(),
                    curve: String::new(),
                },
                if private { "private" } else { "public" }.into(),
            ))
        }
        _ => Err(unsupported()),
    }
}

pub(crate) fn export_jwk(
    data: &[u8],
    name: &str,
    hash: &str,
    key_type: &str,
    curve: &str,
    usages: &[String],
    extractable: bool,
) -> io::Result<serde_json::Value> {
    let mut value = serde_json::Map::new();
    match name {
        "RSA-OAEP" | "RSA-PSS" | "RSASSA-PKCS1-V1_5" => {
            let (n, e) = if key_type == "private" {
                let key = RsaPrivateKey::from_pkcs8_der(data).map_err(io::Error::other)?;
                (key.n().to_bytes_be(), key.e().to_bytes_be())
            } else {
                let key = RsaPublicKey::from_public_key_der(data).map_err(io::Error::other)?;
                (key.n().to_bytes_be(), key.e().to_bytes_be())
            };
            value.insert("kty".into(), "RSA".into());
            value.insert("n".into(), b64(&n).into());
            value.insert("e".into(), b64(&e).into());
            if key_type == "private" {
                let key = RsaPrivateKey::from_pkcs8_der(data).map_err(io::Error::other)?;
                let primes = key.primes();
                if primes.len() != 2 {
                    return Err(unsupported());
                }
                value.insert("d".into(), b64(&key.d().to_bytes_be()).into());
                value.insert("p".into(), b64(&primes[0].to_bytes_be()).into());
                value.insert("q".into(), b64(&primes[1].to_bytes_be()).into());
                value.insert(
                    "dp".into(),
                    b64(&key.dp().ok_or_else(unsupported)?.to_bytes_be()).into(),
                );
                value.insert(
                    "dq".into(),
                    b64(&key.dq().ok_or_else(unsupported)?.to_bytes_be()).into(),
                );
                value.insert(
                    "qi".into(),
                    b64(&key.crt_coefficient().ok_or_else(unsupported)?.to_bytes_be()).into(),
                );
            }
            let prefix = match name {
                "RSA-OAEP" => "RSA-OAEP",
                "RSA-PSS" => "PS",
                _ => "RS",
            };
            let alg = if name == "RSA-OAEP" {
                if hash == "SHA-1" {
                    prefix.into()
                } else {
                    format!("{prefix}-{}", &hash[4..])
                }
            } else {
                format!("{prefix}{}", &hash[4..])
            };
            value.insert("alg".into(), alg.into());
        }
        "ECDSA" | "ECDH" => {
            let (x, y, d) = match (curve, key_type) {
                ("P-256", "private") => {
                    let k = p256::SecretKey::from_pkcs8_der(data).map_err(io::Error::other)?;
                    let p = k.public_key().to_encoded_point(false);
                    (
                        p.x().ok_or_else(unsupported)?.to_vec(),
                        p.y().ok_or_else(unsupported)?.to_vec(),
                        Some(k.to_bytes().to_vec()),
                    )
                }
                ("P-256", _) => {
                    let k = p256::PublicKey::from_public_key_der(data).map_err(io::Error::other)?;
                    let p = k.to_encoded_point(false);
                    (
                        p.x().ok_or_else(unsupported)?.to_vec(),
                        p.y().ok_or_else(unsupported)?.to_vec(),
                        None,
                    )
                }
                ("P-384", "private") => {
                    let k = p384::SecretKey::from_pkcs8_der(data).map_err(io::Error::other)?;
                    let p = k.public_key().to_encoded_point(false);
                    (
                        p.x().ok_or_else(unsupported)?.to_vec(),
                        p.y().ok_or_else(unsupported)?.to_vec(),
                        Some(k.to_bytes().to_vec()),
                    )
                }
                ("P-384", _) => {
                    let k = p384::PublicKey::from_public_key_der(data).map_err(io::Error::other)?;
                    let p = k.to_encoded_point(false);
                    (
                        p.x().ok_or_else(unsupported)?.to_vec(),
                        p.y().ok_or_else(unsupported)?.to_vec(),
                        None,
                    )
                }
                ("P-521", "private") => {
                    let k = p521::SecretKey::from_pkcs8_der(data).map_err(io::Error::other)?;
                    let p = k.public_key().to_encoded_point(false);
                    (
                        p.x().ok_or_else(unsupported)?.to_vec(),
                        p.y().ok_or_else(unsupported)?.to_vec(),
                        Some(k.to_bytes().to_vec()),
                    )
                }
                ("P-521", _) => {
                    let p = p521::PublicKey::from_sec1_bytes(&ec_public_sec1(data)?)
                        .map_err(io::Error::other)?
                        .to_encoded_point(false);
                    (
                        p.x().ok_or_else(unsupported)?.to_vec(),
                        p.y().ok_or_else(unsupported)?.to_vec(),
                        None,
                    )
                }
                _ => return Err(unsupported()),
            };
            value.insert("kty".into(), "EC".into());
            value.insert("crv".into(), curve.into());
            value.insert("x".into(), b64(&x).into());
            value.insert("y".into(), b64(&y).into());
            if let Some(d) = d {
                value.insert("d".into(), b64(&d).into());
            }
            if name == "ECDSA" {
                let alg = match curve {
                    "P-256" => "ES256",
                    "P-384" => "ES384",
                    "P-521" => "ES512",
                    _ => return Err(unsupported()),
                };
                value.insert("alg".into(), alg.into());
            }
        }
        "ED25519" => {
            let (x, d) = if key_type == "private" {
                let k =
                    ed25519_dalek::SigningKey::from_pkcs8_der(data).map_err(io::Error::other)?;
                (
                    k.verifying_key().to_bytes().to_vec(),
                    Some(k.to_bytes().to_vec()),
                )
            } else {
                (
                    ed25519_dalek::VerifyingKey::from_public_key_der(data)
                        .map_err(io::Error::other)?
                        .to_bytes()
                        .to_vec(),
                    None,
                )
            };
            value.insert("kty".into(), "OKP".into());
            value.insert("crv".into(), "Ed25519".into());
            value.insert("x".into(), b64(&x).into());
            if let Some(d) = d {
                value.insert("d".into(), b64(&d).into());
            }
            value.insert("alg".into(), "EdDSA".into());
        }
        "X25519" => {
            let (x, d) = if key_type == "private" {
                let d: [u8; 32] = data
                    .try_into()
                    .map_err(|_| io::Error::other("Invalid key length"))?;
                let s = x25519_dalek::StaticSecret::from(d);
                (
                    x25519_dalek::PublicKey::from(&s).to_bytes().to_vec(),
                    Some(d.to_vec()),
                )
            } else {
                (data.to_vec(), None)
            };
            value.insert("kty".into(), "OKP".into());
            value.insert("crv".into(), "X25519".into());
            value.insert("x".into(), b64(&x).into());
            if let Some(d) = d {
                value.insert("d".into(), b64(&d).into());
            }
        }
        _ => return Err(unsupported()),
    }
    value.insert(
        "key_ops".into(),
        serde_json::to_value(usages).map_err(io::Error::other)?,
    );
    value.insert("ext".into(), extractable.into());
    Ok(value.into())
}

fn mgf1<D>(seed: &[u8], output: &mut [u8])
where
    D: sha2::Digest,
{
    let mut counter = 0u32;
    let mut offset = 0;
    while offset < output.len() {
        let mut hasher = D::new();
        hasher.update(seed);
        hasher.update(counter.to_be_bytes());
        let digest = hasher.finalize();
        let digest = digest.as_slice();
        let take = (output.len() - offset).min(digest.len());
        output[offset..offset + take].copy_from_slice(&digest[..take]);
        offset += take;
        counter = counter.wrapping_add(1);
    }
}

fn oaep_encrypt<D>(public: &RsaPublicKey, label: &[u8], input: &[u8]) -> io::Result<Vec<u8>>
where
    D: sha2::Digest,
{
    let key_size = public.size();
    let hash_size = <D as sha2::Digest>::output_size();
    if input.len() + 2 * hash_size + 2 > key_size {
        return Err(io::Error::other("Invalid RSA-OAEP plaintext length"));
    }
    let db_size = key_size - hash_size - 1;
    let mut db = vec![0; db_size];
    db[..hash_size].copy_from_slice(D::digest(label).as_slice());
    db[db_size - input.len() - 1] = 1;
    db[db_size - input.len()..].copy_from_slice(input);
    let mut seed = Zeroizing::new(vec![0; hash_size]);
    OsRng.fill_bytes(seed.as_mut_slice());
    let mut db_mask = vec![0; db_size];
    mgf1::<D>(&seed, &mut db_mask);
    for (byte, mask) in db.iter_mut().zip(&db_mask) {
        *byte ^= *mask;
    }
    let mut seed_mask = Zeroizing::new(vec![0; hash_size]);
    mgf1::<D>(&db, &mut seed_mask);
    for (byte, mask) in seed.iter_mut().zip(seed_mask.iter()) {
        *byte ^= *mask;
    }
    let mut encoded = Vec::with_capacity(key_size);
    encoded.push(0);
    encoded.extend_from_slice(&seed);
    encoded.extend_from_slice(&db);
    let encoded = rsa::BigUint::from_bytes_be(&encoded);
    let encrypted = rsa_encrypt_raw(public, &encoded).map_err(io::Error::other)?;
    let bytes = encrypted.to_bytes_be();
    if bytes.len() > key_size {
        return Err(io::Error::other("Invalid RSA-OAEP ciphertext"));
    }
    let mut output = vec![0; key_size];
    output[key_size - bytes.len()..].copy_from_slice(&bytes);
    Ok(output)
}

fn oaep_decrypt<D>(private: &RsaPrivateKey, label: &[u8], input: &[u8]) -> io::Result<Vec<u8>>
where
    D: sha2::Digest,
{
    let key_size = private.size();
    let hash_size = <D as sha2::Digest>::output_size();
    if key_size < 2 * hash_size + 2 || input.len() != key_size {
        return Err(io::Error::other("Invalid RSA-OAEP ciphertext"));
    }
    let ciphertext = rsa::BigUint::from_bytes_be(input);
    let mut rng = OsRng;
    let encoded =
        rsa_decrypt_raw(private, Some(&mut rng), &ciphertext).map_err(io::Error::other)?;
    let bytes = encoded.to_bytes_be();
    if bytes.len() > key_size {
        return Err(io::Error::other("Invalid RSA-OAEP ciphertext"));
    }
    let mut padded = Zeroizing::new(vec![0; key_size]);
    padded[key_size - bytes.len()..].copy_from_slice(&bytes);
    let mut failure = (padded[0] != 0) as u8;
    let (masked_seed, masked_db) = padded[1..].split_at(hash_size);
    let mut seed = Zeroizing::new(vec![0; hash_size]);
    let mut seed_mask = vec![0; hash_size];
    mgf1::<D>(masked_db, &mut seed_mask);
    for ((byte, masked), mask) in seed
        .iter_mut()
        .zip(masked_seed.iter())
        .zip(seed_mask.iter())
    {
        *byte = *masked ^ *mask;
    }
    let mut db = Zeroizing::new(vec![0; key_size - hash_size - 1]);
    let mut db_mask = vec![0; db.len()];
    mgf1::<D>(&seed, &mut db_mask);
    for ((byte, masked), mask) in db.iter_mut().zip(masked_db.iter()).zip(db_mask.iter()) {
        *byte = *masked ^ *mask;
    }
    failure |= (!bool::from(db[..hash_size].ct_eq(D::digest(label).as_slice()))) as u8;
    let mut message_start = 0usize;
    let mut looking = 1u8;
    for (index, &byte) in db.iter().enumerate().skip(hash_size) {
        let is_zero = (byte == 0) as u8;
        let is_one = (byte == 1) as u8;
        failure |= looking & (1 - (is_zero | is_one));
        message_start |= (looking & is_one) as usize * (index + 1);
        looking &= 1 - is_one;
    }
    failure |= looking;
    if failure != 0 {
        return Err(io::Error::other("Invalid RSA-OAEP ciphertext"));
    }
    Ok(db[message_start..].to_vec())
}

pub(crate) fn rsa_encrypt(
    name: &str,
    public_der: &[u8],
    hash: &str,
    label: &[u8],
    input: &[u8],
) -> io::Result<Vec<u8>> {
    if name != "RSA-OAEP" {
        return Err(unsupported());
    }
    let key = RsaPublicKey::from_public_key_der(public_der).map_err(io::Error::other)?;
    macro_rules! encrypt {
        ($digest:ty) => {
            oaep_encrypt::<$digest>(&key, label, input)
        };
    }
    match hash {
        "SHA-1" => encrypt!(sha1::Sha1),
        "SHA-256" => encrypt!(sha2::Sha256),
        "SHA-384" => encrypt!(sha2::Sha384),
        "SHA-512" => encrypt!(sha2::Sha512),
        _ => Err(unsupported()),
    }
}

pub(crate) fn rsa_decrypt(
    name: &str,
    private_der: &[u8],
    hash: &str,
    label: &[u8],
    input: &[u8],
) -> io::Result<Vec<u8>> {
    if name != "RSA-OAEP" {
        return Err(unsupported());
    }
    let key = RsaPrivateKey::from_pkcs8_der(private_der).map_err(io::Error::other)?;
    macro_rules! decrypt {
        ($digest:ty) => {
            oaep_decrypt::<$digest>(&key, label, input)
        };
    }
    match hash {
        "SHA-1" => decrypt!(sha1::Sha1),
        "SHA-256" => decrypt!(sha2::Sha256),
        "SHA-384" => decrypt!(sha2::Sha384),
        "SHA-512" => decrypt!(sha2::Sha512),
        _ => Err(unsupported()),
    }
}

pub(crate) fn rsa_sign(
    name: &str,
    private_der: &[u8],
    hash: &str,
    salt_length: usize,
    input: &[u8],
) -> io::Result<Vec<u8>> {
    let hashed = hash_bytes(hash, input)?;
    if name == "RSA-PSS" {
        let mut rng = OsRng;
        macro_rules! sign {
            ($digest:ty) => {{
                let key = RsaPrivateKey::from_pkcs8_der(private_der).map_err(io::Error::other)?;
                let signing_key =
                    rsa::pss::SigningKey::<$digest>::new_with_salt_len(key, salt_length);
                signature::hazmat::RandomizedPrehashSigner::sign_prehash_with_rng(
                    &signing_key,
                    &mut rng,
                    &hashed,
                )
                .map_err(io::Error::other)
                .map(|signature| Box::<[u8]>::from(signature).into_vec())
            }};
        }
        match hash {
            "SHA-1" => sign!(sha1::Sha1),
            "SHA-256" => sign!(sha2::Sha256),
            "SHA-384" => sign!(sha2::Sha384),
            "SHA-512" => sign!(sha2::Sha512),
            _ => Err(unsupported()),
        }
    } else if name == "RSASSA-PKCS1-V1_5" {
        macro_rules! sign {
            ($digest:ty) => {{
                let key = RsaPrivateKey::from_pkcs8_der(private_der).map_err(io::Error::other)?;
                let signing_key = rsa::pkcs1v15::SigningKey::<$digest>::new(key);
                signature::hazmat::PrehashSigner::sign_prehash(&signing_key, &hashed)
                    .map_err(io::Error::other)
                    .map(|signature| Box::<[u8]>::from(signature).into_vec())
            }};
        }
        match hash {
            "SHA-1" => sign!(sha1::Sha1),
            "SHA-256" => sign!(sha2::Sha256),
            "SHA-384" => sign!(sha2::Sha384),
            "SHA-512" => sign!(sha2::Sha512),
            _ => Err(unsupported()),
        }
    } else {
        Err(unsupported())
    }
}

pub(crate) fn rsa_verify(
    name: &str,
    public_der: &[u8],
    hash: &str,
    salt_length: usize,
    input: &[u8],
    signature: &[u8],
) -> io::Result<bool> {
    let hashed = hash_bytes(hash, input)?;
    if name == "RSA-PSS" {
        macro_rules! verify {
            ($digest:ty) => {{
                let key =
                    RsaPublicKey::from_public_key_der(public_der).map_err(io::Error::other)?;
                let verifying_key =
                    rsa::pss::VerifyingKey::<$digest>::new_with_salt_len(key, salt_length);
                let signature = rsa::pss::Signature::try_from(signature)
                    .map_err(|_| io::Error::other("Invalid RSA-PSS signature"))?;
                Ok(signature::hazmat::PrehashVerifier::verify_prehash(
                    &verifying_key,
                    &hashed,
                    &signature,
                )
                .is_ok())
            }};
        }
        match hash {
            "SHA-1" => verify!(sha1::Sha1),
            "SHA-256" => verify!(sha2::Sha256),
            "SHA-384" => verify!(sha2::Sha384),
            "SHA-512" => verify!(sha2::Sha512),
            _ => Err(unsupported()),
        }
    } else if name == "RSASSA-PKCS1-V1_5" {
        macro_rules! verify {
            ($digest:ty) => {{
                let key =
                    RsaPublicKey::from_public_key_der(public_der).map_err(io::Error::other)?;
                let verifying_key = rsa::pkcs1v15::VerifyingKey::<$digest>::new(key);
                let signature = rsa::pkcs1v15::Signature::try_from(signature)
                    .map_err(|_| io::Error::other("Invalid RSASSA-PKCS1-V1_5 signature"))?;
                Ok(signature::hazmat::PrehashVerifier::verify_prehash(
                    &verifying_key,
                    &hashed,
                    &signature,
                )
                .is_ok())
            }};
        }
        match hash {
            "SHA-1" => verify!(sha1::Sha1),
            "SHA-256" => verify!(sha2::Sha256),
            "SHA-384" => verify!(sha2::Sha384),
            "SHA-512" => verify!(sha2::Sha512),
            _ => Err(unsupported()),
        }
    } else {
        Err(unsupported())
    }
}

pub(crate) fn sign(
    name: &str,
    private_der: &[u8],
    hash: &str,
    curve: &str,
    input: &[u8],
) -> io::Result<Vec<u8>> {
    if name == "ED25519" {
        let key =
            ed25519_dalek::SigningKey::from_pkcs8_der(private_der).map_err(io::Error::other)?;
        return Ok(key.sign(input).to_bytes().to_vec());
    }
    macro_rules! sign_curve {
        ($module:ident) => {{
            let key = $module::ecdsa::SigningKey::from_pkcs8_der(private_der)
                .map_err(io::Error::other)?;
            let digest = hash_bytes(hash, input)?;
            let signature: $module::ecdsa::Signature =
                signature::hazmat::PrehashSigner::sign_prehash(&key, &digest)
                    .map_err(io::Error::other)?;
            Ok(signature.to_bytes().to_vec())
        }};
    }
    match (name, curve) {
        ("ECDSA", "P-256") => match hash {
            "SHA-1" => sign_curve!(p256),
            "SHA-256" => sign_curve!(p256),
            "SHA-384" => sign_curve!(p256),
            "SHA-512" => sign_curve!(p256),
            _ => Err(unsupported()),
        },
        ("ECDSA", "P-384") => match hash {
            "SHA-1" => sign_curve!(p384),
            "SHA-256" => sign_curve!(p384),
            "SHA-384" => sign_curve!(p384),
            "SHA-512" => sign_curve!(p384),
            _ => Err(unsupported()),
        },
        ("ECDSA", "P-521") => {
            let private = p521::SecretKey::from_pkcs8_der(private_der).map_err(io::Error::other)?;
            let key = p521::ecdsa::SigningKey::from_slice(private.to_bytes().as_slice())
                .map_err(io::Error::other)?;
            let digest = hash_bytes(hash, input)?;
            let signature: p521::ecdsa::Signature =
                signature::hazmat::PrehashSigner::sign_prehash(&key, &digest)
                    .map_err(io::Error::other)?;
            Ok(signature.to_bytes().to_vec())
        }
        _ => Err(unsupported()),
    }
}

pub(crate) fn verify(
    name: &str,
    public_der: &[u8],
    hash: &str,
    curve: &str,
    input: &[u8],
    signature_bytes: &[u8],
) -> io::Result<bool> {
    if name == "ED25519" {
        let key = ed25519_dalek::VerifyingKey::from_public_key_der(public_der)
            .map_err(io::Error::other)?;
        let Ok(sig) = ed25519_dalek::Signature::from_slice(signature_bytes) else {
            return Ok(false);
        };
        return Ok(key.verify(input, &sig).is_ok());
    }
    macro_rules! verify_curve {
        ($module:ident) => {{
            let key = $module::ecdsa::VerifyingKey::from_public_key_der(public_der)
                .map_err(io::Error::other)?;
            let Ok(sig) = $module::ecdsa::Signature::from_slice(signature_bytes) else {
                return Ok(false);
            };
            let digest = hash_bytes(hash, input)?;
            Ok(signature::hazmat::PrehashVerifier::verify_prehash(&key, &digest, &sig).is_ok())
        }};
    }
    match (name, curve) {
        ("ECDSA", "P-256") => verify_curve!(p256),
        ("ECDSA", "P-384") => verify_curve!(p384),
        ("ECDSA", "P-521") => {
            let info = pkcs8::spki::SubjectPublicKeyInfoRef::try_from(public_der)
                .map_err(io::Error::other)?;
            let encoded = info.subject_public_key.as_bytes().ok_or_else(unsupported)?;
            let key =
                p521::ecdsa::VerifyingKey::from_sec1_bytes(encoded).map_err(io::Error::other)?;
            let Ok(sig) = p521::ecdsa::Signature::from_slice(signature_bytes) else {
                return Ok(false);
            };
            let digest = hash_bytes(hash, input)?;
            Ok(signature::hazmat::PrehashVerifier::verify_prehash(&key, &digest, &sig).is_ok())
        }
        _ => Err(unsupported()),
    }
}

pub(crate) fn ecdh(
    name: &str,
    curve: &str,
    private_der: &[u8],
    public_der: &[u8],
) -> io::Result<Vec<u8>> {
    macro_rules! derive {
        ($module:ident) => {{
            let private =
                $module::SecretKey::from_pkcs8_der(private_der).map_err(io::Error::other)?;
            let public =
                $module::PublicKey::from_public_key_der(public_der).map_err(io::Error::other)?;
            Ok(
                $module::ecdh::diffie_hellman(private.to_nonzero_scalar(), public.as_affine())
                    .raw_secret_bytes()
                    .to_vec(),
            )
        }};
    }
    match (name, curve) {
        ("ECDH", "P-256") => derive!(p256),
        ("ECDH", "P-384") => derive!(p384),
        ("ECDH", "P-521") => {
            let private = p521::SecretKey::from_pkcs8_der(private_der).map_err(io::Error::other)?;
            let info = pkcs8::spki::SubjectPublicKeyInfoRef::try_from(public_der)
                .map_err(io::Error::other)?;
            let encoded = info.subject_public_key.as_bytes().ok_or_else(unsupported)?;
            let public = p521::PublicKey::from_sec1_bytes(encoded).map_err(io::Error::other)?;
            Ok(
                p521::ecdh::diffie_hellman(private.to_nonzero_scalar(), public.as_affine())
                    .raw_secret_bytes()
                    .to_vec(),
            )
        }
        _ => Err(unsupported()),
    }
}

pub(crate) fn x25519(private: &[u8], public: &[u8]) -> io::Result<Vec<u8>> {
    let private: [u8; 32] = private
        .try_into()
        .map_err(|_| io::Error::other("Invalid key length"))?;
    let public: [u8; 32] = public
        .try_into()
        .map_err(|_| io::Error::other("Invalid key length"))?;
    let shared = x25519_dalek::StaticSecret::from(private)
        .diffie_hellman(&x25519_dalek::PublicKey::from(public));
    if !shared.was_contributory() {
        return Err(io::Error::other(
            "X25519 produced an all-zero shared secret",
        ));
    }
    Ok(shared.to_bytes().to_vec())
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn rsa_generation_rejects_invalid_public_exponents_before_keygen() {
        for exponent in [&[0][..], &[1][..], &[2][..], &[1, 0, 2][..]] {
            assert!(generate("RSA-PSS", 1024, exponent, "").is_err());
        }
    }

    #[test]
    fn asymmetric_export_rejects_incompatible_key_types() {
        for (format, key_type) in [("raw", "private"), ("pkcs8", "public"), ("spki", "private")] {
            let error = export_key(format, &[], "ECDSA", key_type, "P-256").unwrap_err();
            assert!(error.to_string().starts_with("InvalidAccessError:"));
        }
    }

    #[test]
    fn rsa_signing_uses_requested_pss_salt_and_pkcs1() {
        let pair = generate("RSA-PSS", 1024, &[1, 0, 1], "").unwrap();
        let message = b"private RSA signatures use OpenSSL";
        let signature = rsa_sign("RSA-PSS", &pair.private, "SHA-256", 32, message).unwrap();
        assert!(rsa_verify("RSA-PSS", &pair.public, "SHA-256", 32, message, &signature).unwrap());
        assert!(!rsa_verify("RSA-PSS", &pair.public, "SHA-256", 20, message, &signature).unwrap());
        let signature =
            rsa_sign("RSASSA-PKCS1-V1_5", &pair.private, "SHA-256", 0, message).unwrap();
        assert!(
            rsa_verify(
                "RSASSA-PKCS1-V1_5",
                &pair.public,
                "SHA-256",
                0,
                message,
                &signature
            )
            .unwrap()
        );
    }
}