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// -*- mode: rust; -*-
//
// This file is part of ed25519-dalek.
// Copyright (c) 2017-2019 isis lovecruft
// See LICENSE for licensing information.
//
// Authors:
// - isis agora lovecruft <isis@patternsinthevoid.net>
//! ed25519 signing keys.
use core::fmt::Debug;
#[cfg(feature = "pkcs8")]
use ed25519::pkcs8;
#[cfg(any(test, feature = "rand_core"))]
use rand_core::CryptoRngCore;
#[cfg(feature = "serde")]
use serde::{Deserialize, Deserializer, Serialize, Serializer};
use sha2::Sha512;
use subtle::{Choice, ConstantTimeEq};
use curve25519_dalek::{
digest::{generic_array::typenum::U64, Digest},
edwards::{CompressedEdwardsY, EdwardsPoint},
scalar::Scalar,
};
use ed25519::signature::{KeypairRef, Signer, Verifier};
#[cfg(feature = "digest")]
use crate::context::Context;
#[cfg(feature = "digest")]
use signature::DigestSigner;
#[cfg(feature = "zeroize")]
use zeroize::{Zeroize, ZeroizeOnDrop};
use crate::{
constants::{KEYPAIR_LENGTH, SECRET_KEY_LENGTH},
errors::{InternalError, SignatureError},
hazmat::ExpandedSecretKey,
signature::InternalSignature,
verifying::VerifyingKey,
Signature,
};
/// ed25519 secret key as defined in [RFC8032 § 5.1.5]:
///
/// > The private key is 32 octets (256 bits, corresponding to b) of
/// > cryptographically secure random data.
///
/// [RFC8032 § 5.1.5]: https://www.rfc-editor.org/rfc/rfc8032#section-5.1.5
pub type SecretKey = [u8; SECRET_KEY_LENGTH];
/// ed25519 signing key which can be used to produce signatures.
// Invariant: `verifying_key` is always the public key of
// `secret_key`. This prevents the signing function oracle attack
// described in https://github.com/MystenLabs/ed25519-unsafe-libs
#[derive(Clone)]
pub struct SigningKey {
/// The secret half of this signing key.
pub(crate) secret_key: SecretKey,
/// The public half of this signing key.
pub(crate) verifying_key: VerifyingKey,
}
/// # Example
///
/// ```
/// # extern crate ed25519_dalek;
/// #
/// use ed25519_dalek::SigningKey;
/// use ed25519_dalek::SECRET_KEY_LENGTH;
/// use ed25519_dalek::SignatureError;
///
/// # fn doctest() -> Result<SigningKey, SignatureError> {
/// let secret_key_bytes: [u8; SECRET_KEY_LENGTH] = [
/// 157, 097, 177, 157, 239, 253, 090, 096,
/// 186, 132, 074, 244, 146, 236, 044, 196,
/// 068, 073, 197, 105, 123, 050, 105, 025,
/// 112, 059, 172, 003, 028, 174, 127, 096, ];
///
/// let signing_key: SigningKey = SigningKey::from_bytes(&secret_key_bytes);
/// assert_eq!(signing_key.to_bytes(), secret_key_bytes);
///
/// # Ok(signing_key)
/// # }
/// #
/// # fn main() {
/// # let result = doctest();
/// # assert!(result.is_ok());
/// # }
/// ```
impl SigningKey {
/// Construct a [`SigningKey`] from a [`SecretKey`]
///
#[inline]
pub fn from_bytes(secret_key: &SecretKey) -> Self {
let verifying_key = VerifyingKey::from(&ExpandedSecretKey::from(secret_key));
Self {
secret_key: *secret_key,
verifying_key,
}
}
/// Convert this [`SigningKey`] into a [`SecretKey`]
#[inline]
pub fn to_bytes(&self) -> SecretKey {
self.secret_key
}
/// Convert this [`SigningKey`] into a [`SecretKey`] reference
#[inline]
pub fn as_bytes(&self) -> &SecretKey {
&self.secret_key
}
/// Construct a [`SigningKey`] from the bytes of a `VerifyingKey` and `SecretKey`.
///
/// # Inputs
///
/// * `bytes`: an `&[u8]` of length [`KEYPAIR_LENGTH`], representing the
/// scalar for the secret key, and a compressed Edwards-Y coordinate of a
/// point on curve25519, both as bytes. (As obtained from
/// [`SigningKey::to_bytes`].)
///
/// # Returns
///
/// A `Result` whose okay value is an EdDSA [`SigningKey`] or whose error value
/// is an `SignatureError` describing the error that occurred.
#[inline]
pub fn from_keypair_bytes(bytes: &[u8; 64]) -> Result<SigningKey, SignatureError> {
let (secret_key, verifying_key) = bytes.split_at(SECRET_KEY_LENGTH);
let signing_key = SigningKey::try_from(secret_key)?;
let verifying_key = VerifyingKey::try_from(verifying_key)?;
if signing_key.verifying_key() != verifying_key {
return Err(InternalError::MismatchedKeypair.into());
}
Ok(signing_key)
}
/// Convert this signing key to a 64-byte keypair.
///
/// # Returns
///
/// An array of bytes, `[u8; KEYPAIR_LENGTH]`. The first
/// `SECRET_KEY_LENGTH` of bytes is the `SecretKey`, and the next
/// `PUBLIC_KEY_LENGTH` bytes is the `VerifyingKey` (the same as other
/// libraries, such as [Adam Langley's ed25519 Golang
/// implementation](https://github.com/agl/ed25519/)). It is guaranteed that
/// the encoded public key is the one derived from the encoded secret key.
pub fn to_keypair_bytes(&self) -> [u8; KEYPAIR_LENGTH] {
let mut bytes: [u8; KEYPAIR_LENGTH] = [0u8; KEYPAIR_LENGTH];
bytes[..SECRET_KEY_LENGTH].copy_from_slice(&self.secret_key);
bytes[SECRET_KEY_LENGTH..].copy_from_slice(self.verifying_key.as_bytes());
bytes
}
/// Get the [`VerifyingKey`] for this [`SigningKey`].
pub fn verifying_key(&self) -> VerifyingKey {
self.verifying_key
}
/// Create a signing context that can be used for Ed25519ph with
/// [`DigestSigner`].
#[cfg(feature = "digest")]
pub fn with_context<'k, 'v>(
&'k self,
context_value: &'v [u8],
) -> Result<Context<'k, 'v, Self>, SignatureError> {
Context::new(self, context_value)
}
/// Generate an ed25519 signing key.
///
/// # Example
///
#[cfg_attr(feature = "rand_core", doc = "```")]
#[cfg_attr(not(feature = "rand_core"), doc = "```ignore")]
/// # fn main() {
/// use rand::rngs::OsRng;
/// use ed25519_dalek::{Signature, SigningKey};
///
/// let mut csprng = OsRng;
/// let signing_key: SigningKey = SigningKey::generate(&mut csprng);
/// # }
/// ```
///
/// # Input
///
/// A CSPRNG with a `fill_bytes()` method, e.g. `rand_os::OsRng`.
///
/// The caller must also supply a hash function which implements the
/// `Digest` and `Default` traits, and which returns 512 bits of output.
/// The standard hash function used for most ed25519 libraries is SHA-512,
/// which is available with `use sha2::Sha512` as in the example above.
/// Other suitable hash functions include Keccak-512 and Blake2b-512.
#[cfg(any(test, feature = "rand_core"))]
pub fn generate<R: CryptoRngCore + ?Sized>(csprng: &mut R) -> SigningKey {
let mut secret = SecretKey::default();
csprng.fill_bytes(&mut secret);
Self::from_bytes(&secret)
}
/// Sign a `prehashed_message` with this [`SigningKey`] using the
/// Ed25519ph algorithm defined in [RFC8032 §5.1][rfc8032].
///
/// # Inputs
///
/// * `prehashed_message` is an instantiated hash digest with 512-bits of
/// output which has had the message to be signed previously fed into its
/// state.
/// * `context` is an optional context string, up to 255 bytes inclusive,
/// which may be used to provide additional domain separation. If not
/// set, this will default to an empty string.
///
/// # Returns
///
/// An Ed25519ph [`Signature`] on the `prehashed_message`.
///
/// # Note
///
/// The RFC only permits SHA-512 to be used for prehashing, i.e., `MsgDigest = Sha512`. This
/// function technically works, and is probably safe to use, with any secure hash function with
/// 512-bit digests, but anything outside of SHA-512 is NOT specification-compliant. We expose
/// [`crate::Sha512`] for user convenience.
///
/// # Examples
///
#[cfg_attr(all(feature = "rand_core", feature = "digest"), doc = "```")]
#[cfg_attr(
any(not(feature = "rand_core"), not(feature = "digest")),
doc = "```ignore"
)]
/// use ed25519_dalek::Digest;
/// use ed25519_dalek::SigningKey;
/// use ed25519_dalek::Signature;
/// use sha2::Sha512;
/// use rand::rngs::OsRng;
///
/// # fn main() {
/// let mut csprng = OsRng;
/// let signing_key: SigningKey = SigningKey::generate(&mut csprng);
/// let message: &[u8] = b"All I want is to pet all of the dogs.";
///
/// // Create a hash digest object which we'll feed the message into:
/// let mut prehashed: Sha512 = Sha512::new();
///
/// prehashed.update(message);
/// # }
/// ```
///
/// If you want, you can optionally pass a "context". It is generally a
/// good idea to choose a context and try to make it unique to your project
/// and this specific usage of signatures.
///
/// For example, without this, if you were to [convert your OpenPGP key
/// to a Bitcoin key][terrible_idea] (just as an example, and also Don't
/// Ever Do That) and someone tricked you into signing an "email" which was
/// actually a Bitcoin transaction moving all your magic internet money to
/// their address, it'd be a valid transaction.
///
/// By adding a context, this trick becomes impossible, because the context
/// is concatenated into the hash, which is then signed. So, going with the
/// previous example, if your bitcoin wallet used a context of
/// "BitcoinWalletAppTxnSigning" and OpenPGP used a context (this is likely
/// the least of their safety problems) of "GPGsCryptoIsntConstantTimeLol",
/// then the signatures produced by both could never match the other, even
/// if they signed the exact same message with the same key.
///
/// Let's add a context for good measure (remember, you'll want to choose
/// your own!):
///
#[cfg_attr(all(feature = "rand_core", feature = "digest"), doc = "```")]
#[cfg_attr(
any(not(feature = "rand_core"), not(feature = "digest")),
doc = "```ignore"
)]
/// # use ed25519_dalek::Digest;
/// # use ed25519_dalek::SigningKey;
/// # use ed25519_dalek::Signature;
/// # use ed25519_dalek::SignatureError;
/// # use sha2::Sha512;
/// # use rand::rngs::OsRng;
/// #
/// # fn do_test() -> Result<Signature, SignatureError> {
/// # let mut csprng = OsRng;
/// # let signing_key: SigningKey = SigningKey::generate(&mut csprng);
/// # let message: &[u8] = b"All I want is to pet all of the dogs.";
/// # let mut prehashed: Sha512 = Sha512::new();
/// # prehashed.update(message);
/// #
/// let context: &[u8] = b"Ed25519DalekSignPrehashedDoctest";
///
/// let sig: Signature = signing_key.sign_prehashed(prehashed, Some(context))?;
/// #
/// # Ok(sig)
/// # }
/// # fn main() {
/// # do_test();
/// # }
/// ```
///
/// [rfc8032]: https://tools.ietf.org/html/rfc8032#section-5.1
/// [terrible_idea]: https://github.com/isislovecruft/scripts/blob/master/gpgkey2bc.py
#[cfg(feature = "digest")]
pub fn sign_prehashed<MsgDigest>(
&self,
prehashed_message: MsgDigest,
context: Option<&[u8]>,
) -> Result<Signature, SignatureError>
where
MsgDigest: Digest<OutputSize = U64>,
{
ExpandedSecretKey::from(&self.secret_key).raw_sign_prehashed::<Sha512, MsgDigest>(
prehashed_message,
&self.verifying_key,
context,
)
}
/// Verify a signature on a message with this signing key's public key.
pub fn verify(&self, message: &[u8], signature: &Signature) -> Result<(), SignatureError> {
self.verifying_key.verify(message, signature)
}
/// Verify a `signature` on a `prehashed_message` using the Ed25519ph algorithm.
///
/// # Inputs
///
/// * `prehashed_message` is an instantiated hash digest with 512-bits of
/// output which has had the message to be signed previously fed into its
/// state.
/// * `context` is an optional context string, up to 255 bytes inclusive,
/// which may be used to provide additional domain separation. If not
/// set, this will default to an empty string.
/// * `signature` is a purported Ed25519ph [`Signature`] on the `prehashed_message`.
///
/// # Returns
///
/// Returns `true` if the `signature` was a valid signature created by this
/// [`SigningKey`] on the `prehashed_message`.
///
/// # Note
///
/// The RFC only permits SHA-512 to be used for prehashing, i.e., `MsgDigest = Sha512`. This
/// function technically works, and is probably safe to use, with any secure hash function with
/// 512-bit digests, but anything outside of SHA-512 is NOT specification-compliant. We expose
/// [`crate::Sha512`] for user convenience.
///
/// # Examples
///
#[cfg_attr(all(feature = "rand_core", feature = "digest"), doc = "```")]
#[cfg_attr(
any(not(feature = "rand_core"), not(feature = "digest")),
doc = "```ignore"
)]
/// use ed25519_dalek::Digest;
/// use ed25519_dalek::SigningKey;
/// use ed25519_dalek::Signature;
/// use ed25519_dalek::SignatureError;
/// use sha2::Sha512;
/// use rand::rngs::OsRng;
///
/// # fn do_test() -> Result<(), SignatureError> {
/// let mut csprng = OsRng;
/// let signing_key: SigningKey = SigningKey::generate(&mut csprng);
/// let message: &[u8] = b"All I want is to pet all of the dogs.";
///
/// let mut prehashed: Sha512 = Sha512::new();
/// prehashed.update(message);
///
/// let context: &[u8] = b"Ed25519DalekSignPrehashedDoctest";
///
/// let sig: Signature = signing_key.sign_prehashed(prehashed, Some(context))?;
///
/// // The sha2::Sha512 struct doesn't implement Copy, so we'll have to create a new one:
/// let mut prehashed_again: Sha512 = Sha512::default();
/// prehashed_again.update(message);
///
/// let verified = signing_key.verifying_key().verify_prehashed(prehashed_again, Some(context), &sig);
///
/// assert!(verified.is_ok());
///
/// # verified
/// # }
/// #
/// # fn main() {
/// # do_test();
/// # }
/// ```
///
/// [rfc8032]: https://tools.ietf.org/html/rfc8032#section-5.1
#[cfg(feature = "digest")]
pub fn verify_prehashed<MsgDigest>(
&self,
prehashed_message: MsgDigest,
context: Option<&[u8]>,
signature: &Signature,
) -> Result<(), SignatureError>
where
MsgDigest: Digest<OutputSize = U64>,
{
self.verifying_key
.verify_prehashed(prehashed_message, context, signature)
}
/// Strictly verify a signature on a message with this signing key's public key.
///
/// # On The (Multiple) Sources of Malleability in Ed25519 Signatures
///
/// This version of verification is technically non-RFC8032 compliant. The
/// following explains why.
///
/// 1. Scalar Malleability
///
/// The authors of the RFC explicitly stated that verification of an ed25519
/// signature must fail if the scalar `s` is not properly reduced mod \ell:
///
/// > To verify a signature on a message M using public key A, with F
/// > being 0 for Ed25519ctx, 1 for Ed25519ph, and if Ed25519ctx or
/// > Ed25519ph is being used, C being the context, first split the
/// > signature into two 32-octet halves. Decode the first half as a
/// > point R, and the second half as an integer S, in the range
/// > 0 <= s < L. Decode the public key A as point A'. If any of the
/// > decodings fail (including S being out of range), the signature is
/// > invalid.)
///
/// All `verify_*()` functions within ed25519-dalek perform this check.
///
/// 2. Point malleability
///
/// The authors of the RFC added in a malleability check to step #3 in
/// §5.1.7, for small torsion components in the `R` value of the signature,
/// *which is not strictly required*, as they state:
///
/// > Check the group equation \[8\]\[S\]B = \[8\]R + \[8\]\[k\]A'. It's
/// > sufficient, but not required, to instead check \[S\]B = R + \[k\]A'.
///
/// # History of Malleability Checks
///
/// As originally defined (cf. the "Malleability" section in the README of
/// this repo), ed25519 signatures didn't consider *any* form of
/// malleability to be an issue. Later the scalar malleability was
/// considered important. Still later, particularly with interests in
/// cryptocurrency design and in unique identities (e.g. for Signal users,
/// Tor onion services, etc.), the group element malleability became a
/// concern.
///
/// However, libraries had already been created to conform to the original
/// definition. One well-used library in particular even implemented the
/// group element malleability check, *but only for batch verification*!
/// Which meant that even using the same library, a single signature could
/// verify fine individually, but suddenly, when verifying it with a bunch
/// of other signatures, the whole batch would fail!
///
/// # "Strict" Verification
///
/// This method performs *both* of the above signature malleability checks.
///
/// It must be done as a separate method because one doesn't simply get to
/// change the definition of a cryptographic primitive ten years
/// after-the-fact with zero consideration for backwards compatibility in
/// hardware and protocols which have it already have the older definition
/// baked in.
///
/// # Return
///
/// Returns `Ok(())` if the signature is valid, and `Err` otherwise.
#[allow(non_snake_case)]
pub fn verify_strict(
&self,
message: &[u8],
signature: &Signature,
) -> Result<(), SignatureError> {
self.verifying_key.verify_strict(message, signature)
}
/// Convert this signing key into a byte representation of an unreduced, unclamped Curve25519
/// scalar. This is NOT the same thing as `self.to_scalar().to_bytes()`, since `to_scalar()`
/// performs a clamping step, which changes the value of the resulting scalar.
///
/// This can be used for performing X25519 Diffie-Hellman using Ed25519 keys. The bytes output
/// by this function are a valid corresponding [`StaticSecret`](https://docs.rs/x25519-dalek/2.0.0/x25519_dalek/struct.StaticSecret.html#impl-From%3C%5Bu8;+32%5D%3E-for-StaticSecret)
/// for the X25519 public key given by `self.verifying_key().to_montgomery()`.
///
/// # Note
///
/// We do NOT recommend using a signing/verifying key for encryption. Signing keys are usually
/// long-term keys, while keys used for key exchange should rather be ephemeral. If you can
/// help it, use a separate key for encryption.
///
/// For more information on the security of systems which use the same keys for both signing
/// and Diffie-Hellman, see the paper
/// [On using the same key pair for Ed25519 and an X25519 based KEM](https://eprint.iacr.org/2021/509).
pub fn to_scalar_bytes(&self) -> [u8; 32] {
// Per the spec, the ed25519 secret key sk is expanded to
// (scalar_bytes, hash_prefix) = SHA-512(sk)
// where the two outputs are both 32 bytes. scalar_bytes is what we return. Its clamped and
// reduced form is what we use for signing (see impl ExpandedSecretKey)
let mut buf = [0u8; 32];
let scalar_and_hash_prefix = Sha512::default().chain_update(self.secret_key).finalize();
buf.copy_from_slice(&scalar_and_hash_prefix[..32]);
buf
}
/// Convert this signing key into a Curve25519 scalar. This is computed by clamping and
/// reducing the output of [`Self::to_scalar_bytes`].
///
/// This can be used anywhere where a Curve25519 scalar is used as a private key, e.g., in
/// [`crypto_box`](https://docs.rs/crypto_box/0.9.1/crypto_box/struct.SecretKey.html#impl-From%3CScalar%3E-for-SecretKey).
///
/// # Note
///
/// We do NOT recommend using a signing/verifying key for encryption. Signing keys are usually
/// long-term keys, while keys used for key exchange should rather be ephemeral. If you can
/// help it, use a separate key for encryption.
///
/// For more information on the security of systems which use the same keys for both signing
/// and Diffie-Hellman, see the paper
/// [On using the same key pair for Ed25519 and an X25519 based KEM](https://eprint.iacr.org/2021/509).
pub fn to_scalar(&self) -> Scalar {
// Per the spec, the ed25519 secret key sk is expanded to
// (scalar_bytes, hash_prefix) = SHA-512(sk)
// where the two outputs are both 32 bytes. To use for signing, scalar_bytes must be
// clamped and reduced (see ExpandedSecretKey::from_bytes). We return the clamped and
// reduced form.
ExpandedSecretKey::from(&self.secret_key).scalar
}
}
impl AsRef<VerifyingKey> for SigningKey {
fn as_ref(&self) -> &VerifyingKey {
&self.verifying_key
}
}
impl Debug for SigningKey {
fn fmt(&self, f: &mut ::core::fmt::Formatter<'_>) -> ::core::fmt::Result {
f.debug_struct("SigningKey")
.field("verifying_key", &self.verifying_key)
.finish_non_exhaustive() // avoids printing `secret_key`
}
}
impl KeypairRef for SigningKey {
type VerifyingKey = VerifyingKey;
}
impl Signer<Signature> for SigningKey {
/// Sign a message with this signing key's secret key.
fn try_sign(&self, message: &[u8]) -> Result<Signature, SignatureError> {
let expanded: ExpandedSecretKey = (&self.secret_key).into();
Ok(expanded.raw_sign::<Sha512>(message, &self.verifying_key))
}
}
/// Equivalent to [`SigningKey::sign_prehashed`] with `context` set to [`None`].
///
/// # Note
///
/// The RFC only permits SHA-512 to be used for prehashing. This function technically works, and is
/// probably safe to use, with any secure hash function with 512-bit digests, but anything outside
/// of SHA-512 is NOT specification-compliant. We expose [`crate::Sha512`] for user convenience.
#[cfg(feature = "digest")]
impl<D> DigestSigner<D, Signature> for SigningKey
where
D: Digest<OutputSize = U64>,
{
fn try_sign_digest(&self, msg_digest: D) -> Result<Signature, SignatureError> {
self.sign_prehashed(msg_digest, None)
}
}
/// Equivalent to [`SigningKey::sign_prehashed`] with `context` set to [`Some`]
/// containing `self.value()`.
///
/// # Note
///
/// The RFC only permits SHA-512 to be used for prehashing. This function technically works, and is
/// probably safe to use, with any secure hash function with 512-bit digests, but anything outside
/// of SHA-512 is NOT specification-compliant. We expose [`crate::Sha512`] for user convenience.
#[cfg(feature = "digest")]
impl<D> DigestSigner<D, Signature> for Context<'_, '_, SigningKey>
where
D: Digest<OutputSize = U64>,
{
fn try_sign_digest(&self, msg_digest: D) -> Result<Signature, SignatureError> {
self.key().sign_prehashed(msg_digest, Some(self.value()))
}
}
impl Verifier<Signature> for SigningKey {
/// Verify a signature on a message with this signing key's public key.
fn verify(&self, message: &[u8], signature: &Signature) -> Result<(), SignatureError> {
self.verifying_key.verify(message, signature)
}
}
impl From<SecretKey> for SigningKey {
#[inline]
fn from(secret: SecretKey) -> Self {
Self::from_bytes(&secret)
}
}
impl From<&SecretKey> for SigningKey {
#[inline]
fn from(secret: &SecretKey) -> Self {
Self::from_bytes(secret)
}
}
impl TryFrom<&[u8]> for SigningKey {
type Error = SignatureError;
fn try_from(bytes: &[u8]) -> Result<SigningKey, SignatureError> {
SecretKey::try_from(bytes)
.map(|bytes| Self::from_bytes(&bytes))
.map_err(|_| {
InternalError::BytesLength {
name: "SecretKey",
length: SECRET_KEY_LENGTH,
}
.into()
})
}
}
impl ConstantTimeEq for SigningKey {
fn ct_eq(&self, other: &Self) -> Choice {
self.secret_key.ct_eq(&other.secret_key)
}
}
impl PartialEq for SigningKey {
fn eq(&self, other: &Self) -> bool {
self.ct_eq(other).into()
}
}
impl Eq for SigningKey {}
#[cfg(feature = "zeroize")]
impl Drop for SigningKey {
fn drop(&mut self) {
self.secret_key.zeroize();
}
}
#[cfg(feature = "zeroize")]
impl ZeroizeOnDrop for SigningKey {}
#[cfg(all(feature = "alloc", feature = "pkcs8"))]
impl pkcs8::EncodePrivateKey for SigningKey {
fn to_pkcs8_der(&self) -> pkcs8::Result<pkcs8::SecretDocument> {
pkcs8::KeypairBytes::from(self).to_pkcs8_der()
}
}
#[cfg(feature = "pkcs8")]
impl TryFrom<pkcs8::KeypairBytes> for SigningKey {
type Error = pkcs8::Error;
fn try_from(pkcs8_key: pkcs8::KeypairBytes) -> pkcs8::Result<Self> {
SigningKey::try_from(&pkcs8_key)
}
}
#[cfg(feature = "pkcs8")]
impl TryFrom<&pkcs8::KeypairBytes> for SigningKey {
type Error = pkcs8::Error;
fn try_from(pkcs8_key: &pkcs8::KeypairBytes) -> pkcs8::Result<Self> {
let signing_key = SigningKey::from_bytes(&pkcs8_key.secret_key);
// Validate the public key in the PKCS#8 document if present
if let Some(public_bytes) = &pkcs8_key.public_key {
let expected_verifying_key = VerifyingKey::from_bytes(public_bytes.as_ref())
.map_err(|_| pkcs8::Error::KeyMalformed)?;
if signing_key.verifying_key() != expected_verifying_key {
return Err(pkcs8::Error::KeyMalformed);
}
}
Ok(signing_key)
}
}
#[cfg(feature = "pkcs8")]
impl From<SigningKey> for pkcs8::KeypairBytes {
fn from(signing_key: SigningKey) -> pkcs8::KeypairBytes {
pkcs8::KeypairBytes::from(&signing_key)
}
}
#[cfg(feature = "pkcs8")]
impl From<&SigningKey> for pkcs8::KeypairBytes {
fn from(signing_key: &SigningKey) -> pkcs8::KeypairBytes {
pkcs8::KeypairBytes {
secret_key: signing_key.to_bytes(),
public_key: Some(pkcs8::PublicKeyBytes(signing_key.verifying_key.to_bytes())),
}
}
}
#[cfg(feature = "pkcs8")]
impl TryFrom<pkcs8::PrivateKeyInfo<'_>> for SigningKey {
type Error = pkcs8::Error;
fn try_from(private_key: pkcs8::PrivateKeyInfo<'_>) -> pkcs8::Result<Self> {
pkcs8::KeypairBytes::try_from(private_key)?.try_into()
}
}
#[cfg(feature = "serde")]
impl Serialize for SigningKey {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: Serializer,
{
serializer.serialize_bytes(&self.secret_key)
}
}
#[cfg(feature = "serde")]
impl<'d> Deserialize<'d> for SigningKey {
fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
where
D: Deserializer<'d>,
{
struct SigningKeyVisitor;
impl<'de> serde::de::Visitor<'de> for SigningKeyVisitor {
type Value = SigningKey;
fn expecting(&self, formatter: &mut ::core::fmt::Formatter<'_>) -> ::core::fmt::Result {
write!(formatter, concat!("An ed25519 signing (private) key"))
}
fn visit_bytes<E: serde::de::Error>(self, bytes: &[u8]) -> Result<Self::Value, E> {
SigningKey::try_from(bytes).map_err(E::custom)
}
fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
where
A: serde::de::SeqAccess<'de>,
{
let mut bytes = [0u8; 32];
#[allow(clippy::needless_range_loop)]
for i in 0..32 {
bytes[i] = seq
.next_element()?
.ok_or_else(|| serde::de::Error::invalid_length(i, &"expected 32 bytes"))?;
}
let remaining = (0..)
.map(|_| seq.next_element::<u8>())
.take_while(|el| matches!(el, Ok(Some(_))))
.count();
if remaining > 0 {
return Err(serde::de::Error::invalid_length(
32 + remaining,
&"expected 32 bytes",
));
}
SigningKey::try_from(bytes).map_err(serde::de::Error::custom)
}
}
deserializer.deserialize_bytes(SigningKeyVisitor)
}
}
/// The spec-compliant way to define an expanded secret key. This computes `SHA512(sk)`, clamps the
/// first 32 bytes and uses it as a scalar, and uses the second 32 bytes as a domain separator for
/// hashing.
impl From<&SecretKey> for ExpandedSecretKey {
#[allow(clippy::unwrap_used)]
fn from(secret_key: &SecretKey) -> ExpandedSecretKey {
let hash = Sha512::default().chain_update(secret_key).finalize();
ExpandedSecretKey::from_bytes(hash.as_ref())
}
}
//
// Signing functions. These are pub(crate) so that the `hazmat` module can use them
//
impl ExpandedSecretKey {
/// The plain, non-prehashed, signing function for Ed25519. `CtxDigest` is the digest used to
/// calculate the pseudorandomness needed for signing. According to the spec, `CtxDigest =
/// Sha512`, and `self` is derived via the method defined in `impl From<&SigningKey> for
/// ExpandedSecretKey`.
///
/// This definition is loose in its parameters so that end-users of the `hazmat` module can
/// change how the `ExpandedSecretKey` is calculated and which hash function to use.
#[allow(non_snake_case)]
#[inline(always)]
pub(crate) fn raw_sign<CtxDigest>(
&self,
message: &[u8],
verifying_key: &VerifyingKey,
) -> Signature
where
CtxDigest: Digest<OutputSize = U64>,
{
let mut h = CtxDigest::new();
h.update(self.hash_prefix);
h.update(message);
let r = Scalar::from_hash(h);
let R: CompressedEdwardsY = EdwardsPoint::mul_base(&r).compress();
h = CtxDigest::new();
h.update(R.as_bytes());
h.update(verifying_key.as_bytes());
h.update(message);
let k = Scalar::from_hash(h);
let s: Scalar = (k * self.scalar) + r;
InternalSignature { R, s }.into()
}
/// The prehashed signing function for Ed25519 (i.e., Ed25519ph). `CtxDigest` is the digest
/// function used to calculate the pseudorandomness needed for signing. `MsgDigest` is the
/// digest function used to hash the signed message. According to the spec, `MsgDigest =
/// CtxDigest = Sha512`, and `self` is derived via the method defined in `impl
/// From<&SigningKey> for ExpandedSecretKey`.
///
/// This definition is loose in its parameters so that end-users of the `hazmat` module can
/// change how the `ExpandedSecretKey` is calculated and which `CtxDigest` function to use.
#[cfg(feature = "digest")]
#[allow(non_snake_case)]
#[inline(always)]
pub(crate) fn raw_sign_prehashed<CtxDigest, MsgDigest>(
&self,
prehashed_message: MsgDigest,
verifying_key: &VerifyingKey,
context: Option<&[u8]>,
) -> Result<Signature, SignatureError>
where
CtxDigest: Digest<OutputSize = U64>,
MsgDigest: Digest<OutputSize = U64>,
{
let mut prehash: [u8; 64] = [0u8; 64];
let ctx: &[u8] = context.unwrap_or(b""); // By default, the context is an empty string.
if ctx.len() > 255 {
return Err(SignatureError::from(InternalError::PrehashedContextLength));
}
let ctx_len: u8 = ctx.len() as u8;
// Get the result of the pre-hashed message.
prehash.copy_from_slice(prehashed_message.finalize().as_slice());
// This is the dumbest, ten-years-late, non-admission of fucking up the
// domain separation I have ever seen. Why am I still required to put
// the upper half "prefix" of the hashed "secret key" in here? Why
// can't the user just supply their own nonce and decide for themselves
// whether or not they want a deterministic signature scheme? Why does
// the message go into what's ostensibly the signature domain separation
// hash? Why wasn't there always a way to provide a context string?
//
// ...
//
// This is a really fucking stupid bandaid, and the damned scheme is
// still bleeding from malleability, for fuck's sake.
let mut h = CtxDigest::new()
.chain_update(b"SigEd25519 no Ed25519 collisions")
.chain_update([1]) // Ed25519ph
.chain_update([ctx_len])
.chain_update(ctx)
.chain_update(self.hash_prefix)
.chain_update(&prehash[..]);
let r = Scalar::from_hash(h);
let R: CompressedEdwardsY = EdwardsPoint::mul_base(&r).compress();
h = CtxDigest::new()
.chain_update(b"SigEd25519 no Ed25519 collisions")
.chain_update([1]) // Ed25519ph
.chain_update([ctx_len])
.chain_update(ctx)
.chain_update(R.as_bytes())
.chain_update(verifying_key.as_bytes())
.chain_update(&prehash[..]);
let k = Scalar::from_hash(h);
let s: Scalar = (k * self.scalar) + r;
Ok(InternalSignature { R, s }.into())
}
}