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Fix P-521 ECDSA verification and add curve coverage tests #1956

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Fix P-521 ECDSA verification and add curve coverage tests #1956

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2386f22
Fix P-521 curve name typo and signature length check in ECDSA verifier
nadahalli Apr 2, 2026
60be6e6
Add COSE Sign1 verification tests against RFC 8152 / cose-wg vectors
nadahalli Apr 2, 2026
997c9ff
Address review: reuse curveKeySize in test, use ecdsa.SignASN1 for DE…
nadahalli Apr 2, 2026
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21 changes: 17 additions & 4 deletions pkg/teeattestation/nitro/verify.go
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Original file line number Diff line number Diff line change
Expand Up @@ -220,14 +220,27 @@ func parseCertificateChain(doc *attestationDocument) (*x509.Certificate, *x509.C
return leafCert, intermediates, nil
}

// curveKeySize returns the byte length of one ECDSA signature component
// (r or s) for the given curve: ceil(bitSize / 8). This is the correct
Comment on lines +223 to +224
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@vreff vreff Apr 2, 2026

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super nit: maybe do float division -> ciel -> cast to int in case this helper is ever required for other curves with odd bit sizes

// size per RFC 9053 section 2.1, and differs from the hash length for P-521
// (key component = 66 bytes, hash = 64 bytes).
func curveKeySize(publicKey *ecdsa.PublicKey) int {
return (publicKey.Curve.Params().BitSize + 7) / 8
}

func verifyECDSASignature(publicKey *ecdsa.PublicKey, sigStructure, signature []byte) bool {
keySize := curveKeySize(publicKey)
if len(signature) != 2*keySize {
return false
}

hash, ok := hashForCurve(publicKey, sigStructure)
if !ok || len(signature) != 2*len(hash) {
if !ok {
return false
}

r := new(big.Int).SetBytes(signature[:len(hash)])
s := new(big.Int).SetBytes(signature[len(hash):])
r := new(big.Int).SetBytes(signature[:keySize])
s := new(big.Int).SetBytes(signature[keySize:])
return ecdsa.Verify(publicKey, hash, r, s)
}

Expand All @@ -242,7 +255,7 @@ func hashForCurve(publicKey *ecdsa.PublicKey, sigStructure []byte) ([]byte, bool
case "P-384":
sum := sha512.Sum384(sigStructure)
return sum[:], true
case "P-512":
case "P-521":
sum := sha512.Sum512(sigStructure)
return sum[:], true
default:
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