initial version with Decrypt

rncryptor.go

@@ -0,0 +1,54 @@
+package rncryptor
+
+import(
+  "bytes"
+  "log"
+  "crypto/sha1"
+  "crypto/sha256"
+  "crypto/hmac"
+  "crypto/aes"
+  "crypto/cipher"
+  "golang.org/x/crypto/pbkdf2"
+)
+
+func Decrypt(text, password []byte) ([]byte) {
+  version         := text[:1]
+  options         := text[1:2]
+  encSalt         := text[2:10]
+  hmacSalt        := text[10:18]
+  iv              := text[18:34]
+  cipherText      := text[34:(len(text)-66+34)]
+  expectedHmac    := text[len(text)-32:len(text)]
+
+  msg := make([]byte, 0)
+  msg = append(msg, version...)
+  msg = append(msg, options...)
+  msg = append(msg, encSalt...)
+  msg = append(msg, hmacSalt...)
+  msg = append(msg, iv...)
+  msg = append(msg, cipherText...)
+
+
+  hmacKey := pbkdf2.Key(password, hmacSalt, 10000, 32, sha1.New)
+
+  testHmac := hmac.New(sha256.New, hmacKey)
+  testHmac.Write(msg)
+  testHmacVal := testHmac.Sum(nil)
+
+  verified := bytes.Equal(testHmacVal, expectedHmac)
+
+  if !verified {
+    log.Fatal("Password may be incorrect, or the data has been corrupted. (HMAC could not be verified)")
+  }
+
+  cipherKey := pbkdf2.Key(password, encSalt, 10000, 32, sha1.New)
+  cipherBlock, err := aes.NewCipher(cipherKey)
+  if err != nil {
+    log.Fatal(err)
+  }
+
+  decrypter := cipher.NewCBCDecrypter(cipherBlock, iv)
+  decrypter.CryptBlocks(cipherText, cipherText)
+
+  return cipherText
+}