ECCRYPTO_STATUS SchnorrQ_Verify()

in FourQ_ARM_NEON/schnorrq.c [134:190]

• 43 lines of code
• 12 McCabe index (conditional complexity)

ECCRYPTO_STATUS SchnorrQ_Verify(const unsigned char* PublicKey, const unsigned char* Message, const unsigned int SizeMessage, const unsigned char* Signature, unsigned int* valid)
{ // SchnorrQ signature verification
  // It verifies the signature Signature of a message Message of size SizeMessage in bytes
  // Inputs: 32-byte PublicKey, 64-byte Signature, and Message of size SizeMessage in bytes
  // Output: true (valid signature) or false (invalid signature)
    point_t A;
    unsigned char *temp, h[64];
    unsigned int i;
    ECCRYPTO_STATUS Status = ECCRYPTO_ERROR_UNKNOWN;  

    *valid = false;

	temp = (unsigned char*)calloc(1, SizeMessage+64);
	if (temp == NULL) {
		Status = ECCRYPTO_ERROR_NO_MEMORY;
		goto cleanup;
	}

    if (((PublicKey[15] & 0x80) != 0) || ((Signature[15] & 0x80) != 0) || (Signature[63] != 0) || ((Signature[62] & 0xC0) != 0)) {  // Are bit128(PublicKey) = bit128(Signature) = 0 and Signature+32 < 2^246?
		Status = ECCRYPTO_ERROR_INVALID_PARAMETER;
		goto cleanup;
    }
    
	Status = decode(PublicKey, A);    // Also verifies that A is on the curve. If it is not, it fails  
    if (Status != ECCRYPTO_SUCCESS) {
        goto cleanup;                            
    }

    memmove(temp, Signature, 32);
    memmove(temp+32, PublicKey, 32);
    memmove(temp+64, Message, SizeMessage);
  
    if (CryptoHashFunction(temp, SizeMessage+64, h) != 0) {   
        Status = ECCRYPTO_ERROR;
        goto cleanup;
    }

    Status = ecc_mul_double((digit_t*)(Signature+32), A, (digit_t*)h, A);      
    if (Status != ECCRYPTO_SUCCESS) {                                                
        goto cleanup;
    }
	
	encode(A, (unsigned char*)A);

    for (i = 0; i < NWORDS_ORDER; i++) {
        if (((digit_t*)A)[i] != ((digit_t*)Signature)[i]) {
            goto cleanup;   
        }
    }
    *valid = true;

cleanup:
	if (temp != NULL)
		free(temp);
    
    return Status;
}