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aes_gcm.go
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aes_gcm.go
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package crypto
import (
"bytes"
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"encoding/base64"
"fmt"
"io"
)
func (crypt *MessageEncryptor) aesGCMEncrypt(value interface{}) (string, error) {
// TODO: check the crypt is properly initiated
k := crypt.Key
// The longest accepted key is 32 byte long,
// instead of rejecting a long key, we truncate it.
// This is how openssl in Ruby works.
if len(k) > 32 {
k = crypt.Key[:32]
}
block, err := aes.NewCipher(k)
if err != nil {
return "", err
}
aesgcm, err := cipher.NewGCM(block)
if err != nil {
return "", err
}
// Set a default serializer if not already set
if crypt.Serializer == nil {
crypt.Serializer = JsonMsgSerializer{}
}
splaintext, err := crypt.Serializer.Serialize(value)
if err != nil {
return "", err
}
plaintext := []byte(splaintext)
iv := make([]byte, aesgcm.NonceSize())
if _, err := io.ReadFull(rand.Reader, iv); err != nil {
return "", err
}
ciphertext := aesgcm.Seal(nil, iv, plaintext, nil)
// Rails stores the GCM auth tag separately from the encrypted data,
// unlike the cipher package, so a little munging is required.
// Luckily aesgcm.Overhead() is the tag size (which is 16).
tagStart := len(ciphertext) - aesgcm.Overhead()
tag := ciphertext[tagStart:]
enc := ciphertext[:tagStart]
vectors := [][]byte{enc, iv, tag}
for i, vec := range vectors {
dst := make([]byte, base64.StdEncoding.EncodedLen(len(vec)))
base64.StdEncoding.Encode(dst, vec)
vectors[i] = dst
}
output := string(bytes.Join(vectors, []byte("--")))
return output, nil
}
func (crypt *MessageEncryptor) aesGCMDecrypt(encryptedMsg string, target interface{}) error {
k := crypt.Key
// The longest accepted key is 32 byte long,
// instead of rejecting a long key, we truncate it.
// This is how openssl in Ruby works.
if len(k) > 32 {
k = crypt.Key[:32]
}
block, err := aes.NewCipher(k)
if err != nil {
return err
}
aesgcm, err := cipher.NewGCM(block)
if err != nil {
return err
}
vectors := bytes.SplitN([]byte(encryptedMsg), []byte("--"), 3)
if len(vectors) != 3 {
return fmt.Errorf("missing vectors, want 3, got %d", len(vectors))
}
for i, vec := range vectors {
dst := make([]byte, base64.StdEncoding.DecodedLen(len(vec)))
n, err := base64.StdEncoding.Decode(dst, vec)
if err != nil {
return fmt.Errorf("bad base64 encoding")
}
vectors[i] = dst[:n]
}
enc := vectors[0]
// Rails splits the auth tag into a separate vector, which is unnecessary really, but fine.
enc = append(enc, vectors[2]...)
nonce := vectors[1]
plain, err := aesgcm.Open(nil, nonce, enc, nil)
if err != nil {
return err
}
return crypt.Serializer.Unserialize(string(plain), target)
}