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Add sign_digest to EcdsaKeyPair to allow signing of pre-digested messages. #915

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Add sign_digest to EcdsaKeyPair to allow signing of pre-digested messages. #915

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95 changes: 95 additions & 0 deletions src/ec/suite_b/ecdsa/signing.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -153,6 +153,8 @@ impl EcdsaKeyPair {

/// Returns the signature of the `message` using a random nonce
/// generated by `rng`.
///
/// The `message` is digested with the appropriate algorithm.
pub fn sign(
&self,
rng: &dyn rand::SecureRandom,
Expand All @@ -163,6 +165,23 @@ impl EcdsaKeyPair {
self.sign_(rng, h)
}

/// Returns the signature of the `digest` using a random nonce
/// generated by `rng`.
///
/// The `digest` algorithm must match that of the signing algorithm.
pub fn sign_digest(
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Please name this sign_digest_less_safe.

Please add a note like the following to the documentation: "In general, it is not safe to sign an arbitrary digest. Ensure that you only sign digests that you have computed yourself, or that you otherwise know are safe to sign. It could be a bad mistake to sign an attacker-controlled digest."

&self,
rng: &dyn rand::SecureRandom,
digest: digest::Digest,
) -> Result<signature::Signature, error::Unspecified> {
// Step 4 (out of order, already performed by caller).
if digest.algorithm() == self.alg.digest_alg {
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Please use the early return style: if ... != ... { return Err(...); }

self.sign_(rng, digest)
} else {
Err(error::Unspecified)
}
}

/// Returns the signature of message digest `h` using a "random" nonce
/// generated by `rng`.
fn sign_(
Expand Down Expand Up @@ -435,6 +454,44 @@ mod tests {
);
}

#[test]
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Tests of the public API should be done in tests/ecdsa_tests.rs.

I suggest that you add a constructor pub(crate) try_from_test_vector to ring::digest::Digest that accepts a digest algorithm and a precomputed value. Then you can rewrite the existing tests to use your new function instead of calling sign_ directly as they currently do.

fn signature_ecdsa_sign_digest_fixed_test() {
test::run(
test_file!("ecdsa_sign_fixed_tests.txt"),
|section, test_case| {
assert_eq!(section, "");

let curve_name = test_case.consume_string("Curve");
let digest_name = test_case.consume_string("Digest");
let msg = test_case.consume_bytes("Msg");
let d = test_case.consume_bytes("d");
let q = test_case.consume_bytes("Q");
let k = test_case.consume_bytes("k");

let expected_result = test_case.consume_bytes("Sig");

let alg = match (curve_name.as_str(), digest_name.as_str()) {
("P-256", "SHA256") => &signature::ECDSA_P256_SHA256_FIXED_SIGNING,
("P-384", "SHA384") => &signature::ECDSA_P384_SHA384_FIXED_SIGNING,
_ => {
panic!("Unsupported curve+digest: {}+{}", curve_name, digest_name);
}
};

let private_key =
signature::EcdsaKeyPair::from_private_key_and_public_key(alg, &d, &q).unwrap();
let rng = test::rand::FixedSliceRandom { bytes: &k };

let digest = crate::digest::digest(alg.digest_alg, &msg);
let actual_result = private_key.sign_digest(&rng, digest).unwrap();

assert_eq!(actual_result.as_ref(), &expected_result[..]);

Ok(())
},
);
}

#[test]
fn signature_ecdsa_sign_asn1_test() {
test::run(
Expand Down Expand Up @@ -471,4 +528,42 @@ mod tests {
},
);
}

#[test]
fn signature_ecdsa_sign_digest_asn1_test() {
test::run(
test_file!("ecdsa_sign_asn1_tests.txt"),
|section, test_case| {
assert_eq!(section, "");

let curve_name = test_case.consume_string("Curve");
let digest_name = test_case.consume_string("Digest");
let msg = test_case.consume_bytes("Msg");
let d = test_case.consume_bytes("d");
let q = test_case.consume_bytes("Q");
let k = test_case.consume_bytes("k");

let expected_result = test_case.consume_bytes("Sig");

let alg = match (curve_name.as_str(), digest_name.as_str()) {
("P-256", "SHA256") => &signature::ECDSA_P256_SHA256_ASN1_SIGNING,
("P-384", "SHA384") => &signature::ECDSA_P384_SHA384_ASN1_SIGNING,
_ => {
panic!("Unsupported curve+digest: {}+{}", curve_name, digest_name);
}
};

let private_key =
signature::EcdsaKeyPair::from_private_key_and_public_key(alg, &d, &q).unwrap();
let rng = test::rand::FixedSliceRandom { bytes: &k };

let digest = crate::digest::digest(alg.digest_alg, &msg);
let actual_result = private_key.sign_digest(&rng, digest).unwrap();

assert_eq!(actual_result.as_ref(), &expected_result[..]);

Ok(())
},
);
}
}