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//! The crypto-backend abstraction.
use crate::{
Error,
Result,
crypto::{
SessionKey,
mem::Protected,
mpi::{MPI, ProtectedMPI},
},
types::{Curve, PublicKeyAlgorithm},
};
/// Abstracts over the cryptographic backends.
pub trait Backend: Asymmetric + Kdf {
/// Returns a short, human-readable description of the backend.
///
/// This starts with the name of the backend, possibly a version,
/// and any optional features that are available. This is meant
/// for inclusion in version strings to improve bug reports.
fn backend() -> String;
/// Fills the given buffer with random data.
///
/// Fills the given buffer with random data produced by a
/// cryptographically secure pseudorandom number generator
/// (CSPRNG). The output may be used as session keys or to derive
/// long-term cryptographic keys from.
fn random(buf: &mut [u8]) -> Result<()>;
}
/// Public-key cryptography interface.
pub trait Asymmetric {
/// Returns whether the given public key cryptography algorithm is
/// supported by this backend.
///
/// Note: when implementing this function, match exhaustively on
/// `algo`, do not use a catch-all. This way, when new algorithms
/// are introduced, we will see where we may need to add support.
fn supports_algo(algo: PublicKeyAlgorithm) -> bool;
/// Returns whether the given elliptic curve is supported by this
/// backend.
///
/// Note: when implementing this function, match exhaustively on
/// `curve`, do not use a catch-all. This way, when new algorithms
/// are introduced, we will see where we may need to add support.
fn supports_curve(curve: &Curve) -> bool;
/// Generates an X25519 key pair.
///
/// Returns a tuple containing the secret and public key.
fn x25519_generate_key() -> Result<(Protected, [u8; 32])>;
/// Clamp the X25519 secret key scalar.
///
/// X25519 does the clamping implicitly, but OpenPGP's ECDH over
/// Curve25519 requires the secret to be clamped. To increase
/// compatibility with OpenPGP implementations that do not
/// implicitly clamp the secrets before use, we do that before we
/// store the secrets in OpenPGP data structures.
///
/// Note: like every function in this trait, this function expects
/// `secret` to be in native byte order.
fn x25519_clamp_secret(secret: &mut Protected) {
secret[0] &= 0b1111_1000;
secret[31] &= !0b1000_0000;
secret[31] |= 0b0100_0000;
}
/// Computes the public key for a given secret key.
fn x25519_derive_public(secret: &Protected) -> Result<[u8; 32]>;
/// Computes the shared point.
fn x25519_shared_point(secret: &Protected, public: &[u8; 32])
-> Result<Protected>;
/// Generates an Ed25519 key pair.
///
/// Returns a tuple containing the secret and public key.
fn ed25519_generate_key() -> Result<(Protected, [u8; 32])>;
/// Computes the public key for a given secret key.
fn ed25519_derive_public(secret: &Protected) -> Result<[u8; 32]>;
/// Creates an Ed25519 signature.
fn ed25519_sign(secret: &Protected, public: &[u8; 32], digest: &[u8])
-> Result<[u8; 64]>;
/// Verifies an Ed25519 signature.
fn ed25519_verify(public: &[u8; 32], digest: &[u8], signature: &[u8; 64])
-> Result<bool>;
/// Generates a DSA key pair.
///
/// `p_bits` denotes the desired size of the parameter `p`.
/// Returns a tuple containing the parameters `p`, `q`, `g`, the
/// public key `y`, and the secret key `x`.
fn dsa_generate_key(p_bits: usize)
-> Result<(MPI, MPI, MPI, MPI, ProtectedMPI)>;
/// Generates an ElGamal key pair.
///
/// `p_bits` denotes the desired size of the parameter `p`.
/// Returns a tuple containing the parameters `p`, `g`, the public
/// key `y`, and the secret key `x`.
fn elgamal_generate_key(p_bits: usize)
-> Result<(MPI, MPI, MPI, ProtectedMPI)> {
let _ = p_bits;
Err(Error::UnsupportedPublicKeyAlgorithm(
PublicKeyAlgorithm::ElGamalEncrypt).into())
}
}
#[cfg(test)]
mod tests {
use crate::crypto::backend::{Backend, interface::Asymmetric};
#[test]
pub fn ed25519_generate_key_private_and_public_not_equal() {
let (secret, public) = Backend::ed25519_generate_key().unwrap();
assert_ne!(secret.as_ref(), public);
}
}
/// Key-Derivation-Functions.
pub trait Kdf {
/// HKDF instantiated with SHA256.
///
/// Used to derive message keys from session keys, and key
/// encapsulating keys from S2K mechanisms. In both cases, using
/// a KDF that includes algorithm information in the given `info`
/// provides key space separation between cipher algorithms and
/// modes.
///
/// `salt`, if given, SHOULD be 32 bytes of salt matching the
/// digest size of the hash function. If it is not give, 32 zeros
/// are used instead.
///
/// `okm` must not be larger than 255 * 32 (the size of the hash
/// digest).
fn hkdf_sha256(ikm: &SessionKey, salt: Option<&[u8]>, info: &[u8],
okm: &mut SessionKey) -> Result<()>;
}
|
