tests: add coverage for exact-size DER signature serialization
What the developer wrote
Authored by Bruno Garcia
tests: add coverage for exact-size DER signature serialization
The existing tests only serialize into oversized buffers or one that is
far too small, so the boundary case where the output buffer is exactly
the required size was untested. Check that this succeeds with identical
output, and that one byte less fails while reporting the required size.
What changed, and why it matters
This commit only adds a new test case. It checks that a DER signature can be written into a buffer that is exactly the right size, and that writing into a buffer one byte too small fails correctly. There is no change to the actual library code that handles signatures, so this does not fix or introduce a security issue by itself.
No security action needed; treat as routine test-coverage improvement. If reviewing a larger series, consider whether this test was added because a prior commit changed serialization behavior.
Security signals we found
No strong security signals were identified.
Evidence from the diff
The diff adds a boundary-condition test in src/tests.c inside test_ecdsa_end_to_end. It serializes a parsed DER ECDSA signature into a 74-byte buffer, confirms the length matches the original, compares bytes, then retries with a buffer length one byte smaller and verifies the function returns 0 while still reporting the required size. The underlying serialization function is unchanged.
Changed components
src/tests.cInspect captured patch +12 / −0
### src/tests.c
@@ -6828,6 +6828,18 @@ static void test_ecdsa_end_to_end(void) {
memset(&signature[0], 0, sizeof(signature[0]));
CHECK(secp256k1_ecdsa_signature_parse_der(CTX, &signature[0], sig, siglen) == 1);
CHECK(secp256k1_ecdsa_verify(CTX, &signature[0], message, &pubkey) == 1);
+ /* Serializing into a buffer of exactly the required size succeeds and
+ * yields the same encoding; one byte less fails and reports the size. */
+ {
+ unsigned char sig2[74];
+ size_t siglen2 = siglen;
+ CHECK(secp256k1_ecdsa_signature_serialize_der(CTX, sig2, &siglen2, &signature[0]) == 1);
+ CHECK(siglen2 == siglen);
+ CHECK(secp256k1_memcmp_var(sig2, sig, siglen) == 0);
+ siglen2 = siglen - 1;
+ CHECK(secp256k1_ecdsa_signature_serialize_der(CTX, sig2, &siglen2, &signature[0]) == 0);
+ CHECK(siglen2 == siglen);
+ }
/* Serialize/destroy/parse DER and verify again. */
siglen = 74;
CHECK(secp256k1_ecdsa_signature_serialize_der(CTX, sig, &siglen, &signature[0]) == 1);Why this scored 13/100
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