dsa: decouple precise RNG state from tests (#1139)

The `signature` test was too tightly coupled with the precise RNG
output, in effect not just testing the DSA signature/verification logic
but also testing that the exact bit sequence was produced by the
dependent crate.

We already have tests against deterministic keys and signatures at
`tests/deterministic.rs`, so modify `tests/signature.rs` to instead
generate a random keypair using the system RNG, then generate a
signature with that keypair, and then verify that signature.

The existing hard-coded signatures have been left in place as they are
used to test PKCS decoding and encoding.

Cargo.lock

@@ -371,6 +371,7 @@ dependencies = [
  "hex-literal",
  "pkcs8",
  "proptest",
+ "rand_core 0.10.0-rc-3",
  "rfc6979",
  "sha1",
  "sha2",

dsa/Cargo.toml

@@ -37,6 +37,7 @@ proptest = "1"
 getrandom = { version = "0.4.0-rc.0", features = ["sys_rng"] }
 sha1 = "0.11.0-rc.2"
 der = { version = "0.8.0-rc.10", features = ["derive"] }
+rand_core = "0.10.0-rc-3"
 
 [features]
 default = ["pkcs8"]

dsa/tests/signature.rs

@@ -1,34 +1,28 @@
 #![cfg(feature = "hazmat")]
 #![allow(deprecated)]
 
-use chacha20::{ChaCha8Rng, rand_core::SeedableRng};
 use digest::Digest;
 use dsa::{Components, KeySize, Signature, SigningKey};
-use getrandom::rand_core::CryptoRng;
 use hex_literal::hex;
 use pkcs8::der::{Decode, Encode};
+use rand_core::TryRngCore;
 use sha2::Sha256;
 use signature::{
     DigestVerifier, RandomizedDigestSigner, Signer, Verifier,
     hazmat::{PrehashSigner, PrehashVerifier},
 };
 
-/// Seed used for the ChaCha8 RNG
-const SEED: u64 = 0x2103_1949;
-
 /// Message to be signed/verified
 const MESSAGE: &[u8] = b"test";
 
-/// Message signed by this crate using the keys generated by this CSPRNG
-///
-/// This signature was generated using the keys generated by this CSPRNG (the per-message `k` component was also generated using the CSPRNG)
+/// Message signed by this crate
 const MESSAGE_SIGNATURE_CRATE_ASN1: &[u8] = &[
     0x30, 0x2c, 0x2, 0x14, 0x4e, 0x12, 0x27, 0x75, 0x18, 0xf6, 0x40, 0xe3, 0x3a, 0xdb, 0x80, 0x6d,
     0xe7, 0x98, 0xd3, 0xa3, 0x40, 0xf5, 0x9d, 0xf, 0x2, 0x14, 0x17, 0x78, 0x1e, 0xc8, 0x53, 0x58,
     0x91, 0xe0, 0x3f, 0x2d, 0x36, 0x27, 0x36, 0x6b, 0xac, 0x8e, 0xd7, 0xf9, 0xa4, 0xcf,
 ];
 
-/// Message signed by OpenSSL using the keys generated by this CSPRNG
+/// Message signed by OpenSSL
 ///
 /// This signature was generated using the SHA-256 digest
 const MESSAGE_SIGNATURE_OPENSSL_ASN1: &[u8] = &hex!(
@@ -37,14 +31,9 @@ const MESSAGE_SIGNATURE_OPENSSL_ASN1: &[u8] = &hex!(
      9925 a1d1 7bb8 c835 ca27 0931 ca6a"
 );
 
-/// Get the seeded CSPRNG
-fn seeded_csprng() -> impl CryptoRng {
-    ChaCha8Rng::seed_from_u64(SEED)
-}
-
-/// Generate a DSA keypair using a seeded CSPRNG
-fn generate_deterministic_keypair() -> SigningKey {
-    let mut rng = seeded_csprng();
+/// Generate a random DSA keypair
+fn generate_random_keypair() -> SigningKey {
+    let mut rng = getrandom::SysRng.unwrap_err();
     let components = Components::generate(&mut rng, KeySize::DSA_1024_160);
     SigningKey::generate(&mut rng, components)
 }
@@ -69,35 +58,21 @@ fn decode_encode_signature() {
 }
 
 #[test]
-fn sign_message() {
-    let signing_key = generate_deterministic_keypair();
-    let generated_signature = signing_key
-        .sign_digest_with_rng(&mut seeded_csprng(), |digest: &mut Sha256| {
-            digest.update(MESSAGE)
-        });
-
-    let expected_signature =
-        Signature::from_der(MESSAGE_SIGNATURE_CRATE_ASN1).expect("Failed to decode signature");
-
-    assert_eq!(generated_signature, expected_signature);
-}
-
-#[test]
-fn verify_signature() {
-    let signing_key = generate_deterministic_keypair();
-    let verifying_key = signing_key.verifying_key();
-
-    let signature = Signature::from_der(MESSAGE_SIGNATURE_OPENSSL_ASN1)
-        .expect("Failed to parse ASN.1 representation of the test signature");
+fn sign_verify_message() {
+    let signing_key = generate_random_keypair();
+    let mut rng = getrandom::SysRng.unwrap_err();
+    let generated_signature =
+        signing_key.sign_digest_with_rng(&mut rng, |digest: &mut Sha256| digest.update(MESSAGE));
 
     assert!(
-        verifying_key
+        signing_key
+            .verifying_key()
             .verify_digest(
                 |digest: &mut Sha256| {
                     digest.update(MESSAGE);
                     Ok(())
                 },
-                &signature
+                &generated_signature
             )
             .is_ok()
     );
@@ -105,7 +80,7 @@ fn verify_signature() {
 
 #[test]
 fn signer_verifier_signature() {
-    let signing_key = generate_deterministic_keypair();
+    let signing_key = generate_random_keypair();
     let verifying_key = signing_key.verifying_key();
     let message = b"Hello world! This is the message signed as part of the testing process.";
 
@@ -135,7 +110,7 @@ fn signer_verifier_signature() {
 fn verify_signature_precision() {
     use der::{Sequence, asn1::Uint};
 
-    let signing_key = generate_deterministic_keypair();
+    let signing_key = generate_random_keypair();
     let verifying_key = signing_key.verifying_key();
 
     #[derive(Sequence)]