private bool VerifySignature()

in TPM Parser/Tpm2Lib/CryptoAsym.cs [403:464]
55 lines of code
13 McCabe index (conditional complexity)

        private bool VerifySignature(byte[] data, bool dataIsDigest, ISignatureUnion signature, TpmAlgId sigHash)
        {
            var rsaParams = PublicParms.parameters as RsaParms;
            if (rsaParams != null)
            {
                var sig = signature as SignatureRsa;
                TpmAlgId sigScheme = sig.GetUnionSelector();
                TpmAlgId keyScheme = rsaParams.scheme.GetUnionSelector();

                if (keyScheme != TpmAlgId.Null && keyScheme != sigScheme)
                {
                    Globs.Throw<ArgumentException>("Key scheme and signature scheme do not match");
                    return false;
                }
                if (sigHash == TpmAlgId.Null)
                {
                    sigHash = (rsaParams.scheme as SchemeHash).hashAlg;
                }
                if (sigHash != sig.hash)
                {
                    Globs.Throw<ArgumentException>("Key scheme hash and signature scheme hash do not match");
                    return false;
                }

                byte[] digest = dataIsDigest ? data : CryptoLib.HashData(sigHash, data);

                if (sigScheme == TpmAlgId.Rsassa)
                {
                    return CryptographicEngine.VerifySignatureWithHashInput(Key, CryptographicBuffer.CreateFromByteArray(digest), CryptographicBuffer.CreateFromByteArray(sig.sig));
                }
                if (sigScheme == TpmAlgId.Rsapss)
                {
                    Globs.Throw<ArgumentException>("VerifySignature(): PSS scheme is not supported");
                    return false;
                }
                Globs.Throw<ArgumentException>("VerifySignature(): Unrecognized scheme");
                return false;
            }

            var eccParms = PublicParms.parameters as EccParms;
            if (eccParms != null)
            {
                if (eccParms.scheme.GetUnionSelector() != TpmAlgId.Ecdsa)
                {
                    Globs.Throw<ArgumentException>("Unsupported ECC sig scheme");
                    return false;
                }
                if (sigHash == TpmAlgId.Null)
                {
                    sigHash = (eccParms.scheme as SigSchemeEcdsa).hashAlg;
                }

                byte[] digest = dataIsDigest ? data : CryptoLib.HashData(sigHash, data);
                var sig = signature as SignatureEcdsa;
                byte[] sigBlob = Globs.Concatenate(sig.signatureR, sig.signatureS);
                return CryptographicEngine.VerifySignatureWithHashInput(Key, CryptographicBuffer.CreateFromByteArray(digest), CryptographicBuffer.CreateFromByteArray(sigBlob));
            }

            // Should never be here
            Globs.Throw("VerifySignature: Unrecognized asymmetric algorithm");
            return false;
        } // VerifySignature()