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Add support for Ed25519 to CMS
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Contrary to RSA and ECDSA that take a SHA digest of the message as their input, Ed25519 uses the original message when computing the signature. For this reason, no digest algorithm was previously defined for the Ed25519 signature algorithm. However CMS requires a digest algorithm to be present in the SignerInfo. Therefore creating a CMS signature using a Ed25519 private key would previously fail.

Per RFC 8419 section 2.3, "When signing with Ed25519, the message digest algorithm MUST be SHA-512".

AlgorithmIdentifier.init(digestAlgorithmFor:) has been updated accordingly.

Signature operations have been updated to delegate the validation of the signature algorithm and the computation of the message digest (when relevant) to the underlying key.
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@baarde
baarde committed Jan 17, 2025
1 parent 88ced31 commit d747208
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Showing 7 changed files with 404 additions and 362 deletions.
71 changes: 7 additions & 64 deletions Sources/X509/CertificatePrivateKey.swift
View file
Original file line number Diff line number Diff line change
Expand Up @@ -91,32 +91,23 @@ extension Certificate {
bytes: Bytes,
signatureAlgorithm: SignatureAlgorithm
) throws -> Signature {
try self.validateAlgorithmForKey(algorithm: signatureAlgorithm)

switch self.backing {
case .p256(let p256):
let digestAlgorithm = try AlgorithmIdentifier(digestAlgorithmFor: signatureAlgorithm)
return try p256.signature(for: bytes, digestAlgorithm: digestAlgorithm)
return try p256.signature(for: bytes, signatureAlgorithm: signatureAlgorithm)
case .p384(let p384):
let digestAlgorithm = try AlgorithmIdentifier(digestAlgorithmFor: signatureAlgorithm)
return try p384.signature(for: bytes, digestAlgorithm: digestAlgorithm)
return try p384.signature(for: bytes, signatureAlgorithm: signatureAlgorithm)
case .p521(let p521):
let digestAlgorithm = try AlgorithmIdentifier(digestAlgorithmFor: signatureAlgorithm)
return try p521.signature(for: bytes, digestAlgorithm: digestAlgorithm)
return try p521.signature(for: bytes, signatureAlgorithm: signatureAlgorithm)
case .rsa(let rsa):
let digestAlgorithm = try AlgorithmIdentifier(digestAlgorithmFor: signatureAlgorithm)
let padding = try _RSA.Signing.Padding(forSignatureAlgorithm: signatureAlgorithm)
return try rsa.signature(for: bytes, digestAlgorithm: digestAlgorithm, padding: padding)
return try rsa.signature(for: bytes, signatureAlgorithm: signatureAlgorithm)
#if canImport(Darwin)
case .secureEnclaveP256(let secureEnclaveP256):
let digestAlgorithm = try AlgorithmIdentifier(digestAlgorithmFor: signatureAlgorithm)
return try secureEnclaveP256.signature(for: bytes, digestAlgorithm: digestAlgorithm)
return try secureEnclaveP256.signature(for: bytes, signatureAlgorithm: signatureAlgorithm)
case .secKey(let secKeyWrapper):
let digestAlgorithm = try AlgorithmIdentifier(digestAlgorithmFor: signatureAlgorithm)
return try secKeyWrapper.signature(for: bytes, digestAlgorithm: digestAlgorithm)
return try secKeyWrapper.signature(for: bytes, signatureAlgorithm: signatureAlgorithm)
#endif
case .ed25519(let ed25519):
return try ed25519.signature(for: bytes)
return try ed25519.signature(for: bytes, signatureAlgorithm: signatureAlgorithm)
}
}

Expand All @@ -143,54 +134,6 @@ extension Certificate {
return PublicKey(ed25519.publicKey)
}
}

@inlinable
func validateAlgorithmForKey(algorithm: SignatureAlgorithm) throws {
switch self.backing {
case .p256, .p384, .p521:
if !algorithm.isECDSA {
throw CertificateError.unsupportedSignatureAlgorithm(
reason: "Cannot use \(algorithm) with ECDSA key \(self)"
)
}
case .rsa:
if !algorithm.isRSA {
throw CertificateError.unsupportedSignatureAlgorithm(
reason: "Cannot use \(algorithm) with RSA key \(self)"
)
}
#if canImport(Darwin)
case .secureEnclaveP256:
if !algorithm.isECDSA {
throw CertificateError.unsupportedSignatureAlgorithm(
reason: "Cannot use \(algorithm) with ECDSA key \(self)"
)
}
case .secKey(let key):
switch key.type {
case .ECDSA:
if !algorithm.isECDSA {
throw CertificateError.unsupportedSignatureAlgorithm(
reason: "Cannot use \(algorithm) with ECDSA key \(self)"
)
}
case .RSA:
if !algorithm.isRSA {
throw CertificateError.unsupportedSignatureAlgorithm(
reason: "Cannot use \(algorithm) with RSA key \(self)"
)
}
}
#endif
case .ed25519:
if algorithm != .ed25519 {
throw CertificateError.unsupportedSignatureAlgorithm(
reason: "Cannot use \(algorithm) with Ed25519 key \(self)"
)
}
}

}
}
}

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52 changes: 11 additions & 41 deletions Sources/X509/CertificatePublicKey.swift
View file
Original file line number Diff line number Diff line change
Expand Up @@ -137,32 +137,17 @@ extension Certificate.PublicKey {
for bytes: Bytes,
signatureAlgorithm: Certificate.SignatureAlgorithm
) -> Bool {
var digest: Digest?

if let digestAlgorithm = try? AlgorithmIdentifier(digestAlgorithmFor: signatureAlgorithm) {
digest = try? Digest.computeDigest(for: bytes, using: digestAlgorithm)
}

switch (self.backing, digest) {
case (.p256(let p256), .some(let digest)):
return p256.isValidSignature(signature, for: digest)
case (.p384(let p384), .some(let digest)):
return p384.isValidSignature(signature, for: digest)
case (.p521(let p521), .some(let digest)):
return p521.isValidSignature(signature, for: digest)
case (.rsa(let rsa), .some(let digest)):
// For now we don't support RSA PSS, as it's not deployed in the WebPKI.
// We could, if there are sufficient user needs.
do {
let padding = try _RSA.Signing.Padding(forSignatureAlgorithm: signatureAlgorithm)
return rsa.isValidSignature(signature, for: digest, padding: padding)
} catch {
return false
}
case (.ed25519(let ed25519), .none):
return ed25519.isValidSignature(signature, for: bytes)
default:
return false
switch self.backing {
case .p256(let p256):
return p256.isValidSignature(signature, for: bytes, signatureAlgorithm: signatureAlgorithm)
case .p384(let p384):
return p384.isValidSignature(signature, for: bytes, signatureAlgorithm: signatureAlgorithm)
case .p521(let p521):
return p521.isValidSignature(signature, for: bytes, signatureAlgorithm: signatureAlgorithm)
case .rsa(let rsa):
return rsa.isValidSignature(signature, for: bytes, signatureAlgorithm: signatureAlgorithm)
case .ed25519(let ed25519):
return ed25519.isValidSignature(signature, for: bytes, signatureAlgorithm: signatureAlgorithm)
}
}
}
Expand Down Expand Up @@ -277,21 +262,6 @@ extension Certificate.PublicKey {
}
}

extension _RSA.Signing.Padding {
@inlinable
init(forSignatureAlgorithm signatureAlgorithm: Certificate.SignatureAlgorithm) throws {
switch signatureAlgorithm {
case .sha1WithRSAEncryption, .sha256WithRSAEncryption, .sha384WithRSAEncryption, .sha512WithRSAEncryption:
self = .insecurePKCS1v1_5
default:
// Either this is RSA PSS, or we hit a bug. Either way, unsupported.
throw CertificateError.unsupportedSignatureAlgorithm(
reason: "Unable to determine RSA padding mode for \(signatureAlgorithm)"
)
}
}
}

extension P256.Signing.PublicKey {
/// Create a P256 Public Key from a given ``Certificate/PublicKey-swift.struct``.
///
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