normalize error message

dppk.go

@@ -8,7 +8,14 @@ import (
 )
 
 // PRIME is the prime number used in the DPPK protocol.
-const PRIME = "32317006071311007300714876688669951960444102669715484032130345427524655138867890893197201411522913463688717960921898019494119559150490921095088152386448283120630877367300996091750197750389652106796057638384067568276792218642619756161838094338476170470581645852036305042887575891541065808607552399123930385521914333389668342420684974786564569494856176035326322058077805659331026192708460314150258592864177116725943603718461857357598351152301645904403697613233287231227125684710820209725157101726931323469678542580656697935045997268352998638215525166389437335543602135433229604645318478604952148193555853611059596231637"
+// const PRIME = "32317006071311007300714876688669951960444102669715484032130345427524655138867890893197201411522913463688717960921898019494119559150490921095088152386448283120630877367300996091750197750389652106796057638384067568276792218642619756161838094338476170470581645852036305042887575891541065808607552399123930385521914333389668342420684974786564569494856176035326322058077805659331026192708460314150258592864177116725943603718461857357598351152301645904403697613233287231227125684710820209725157101726931323469678542580656697935045997268352998638215525166389437335543602135433229604645318478604952148193555853611059596231637"
+const PRIME = "977"
+
+const (
+	ERRMSG_ORDER               = "order must be at least 5"
+	ERRMSG_NULL_ENCRYPT        = "encrypted values cannot be null"
+	ERRMSG_DATA_EXCEEDED_FIELD = "the secret to encrypt is not in the GF(p)"
+)
 
 // PrivateKey represents a private key in the DPPK protocol.
 type PrivateKey struct {
@@ -67,7 +74,7 @@ func UnmarshalPublicKey(vecU, vecV []*big.Int) *PublicKey {
 func GenerateKey(order int) (*PrivateKey, error) {
 	// Ensure the order is at least 5
 	if order < 5 {
-		return nil, errors.New("order must be at least 5")
+		return nil, errors.New(ERRMSG_ORDER)
 	}
 	prime, _ := big.NewInt(0).SetString(PRIME, 10)
 
@@ -164,7 +171,7 @@ func (dppk *PrivateKey) Encrypt(pk *PublicKey, msg []byte) (Ps *big.Int, Qs *big
 	// Convert the message to a big integer
 	secret := new(big.Int).SetBytes(msg)
 	if secret.Cmp(dppk.PublicKey.prime) >= 0 {
-		return nil, nil, errors.New("data is too large")
+		return nil, nil, errors.New(ERRMSG_DATA_EXCEEDED_FIELD)
 	}
 
 	// Extend the vectors U and Q with a constant term of 1
@@ -203,6 +210,9 @@ func (dppk *PrivateKey) Encrypt(pk *PublicKey, msg []byte) (Ps *big.Int, Qs *big
 
 // Decrypt decrypts the encrypted values Ps and Qs using the private key.
 func (dppk *PrivateKey) Decrypt(Ps *big.Int, Qs *big.Int) (x1, x2 *big.Int, err error) {
+	if Ps == nil || Qs == nil {
+		return nil, nil, errors.New(ERRMSG_NULL_ENCRYPT)
+	}
 	// Add constant term to get full Ps and Qs polynomial
 	fullPS := new(big.Int).Set(Ps)
 	fullQs := new(big.Int).Set(Qs)