Decrypt[] will yield an error if one tries to decrypt a byte array using a different symmetric key than the one used to encrypt:

Decrypt[key2, Encrypt[key1, "foobar"]["Data"]]
> [..] Decrypt: Data could not be decrypted
> $Failed

I want to be able to mathematically perform the decrypt operation on a byte array and get a byte array even if the key doesn't match, for example, in 3DES. How can I force Decrypt to not yield a message and return the "decrypted" bytes? How does it even know that the decryption is correct or not with no knowledge of the plaintext bytes?


1 Answer 1


From the documentation:

Encrypt[key,"string"] yields an EncryptedObject containing the encrypted version of the contents of the string as encoded in UTF-8.

So the decrypted string must be valid UTF-8. However:

Encrypt[key,ByteArray[...]] yields an EncryptedObject containing the encrypted version of the raw bytes in the ByteArray object.

so if the encrypted thing is a ByteArray, it may work.

  • $\begingroup$ Nope, if you pass a ByteArray output from Encrypt[] it still fails: cryptMethod = <|"Cipher" -> "DES", "BlockMode" -> "ECB", "InitializationVector" -> None|>; Decrypt[GenerateSymmetricKey[Method -> cryptMethod], ByteArray[{77, 232, 217, 172, 56, 169, 190, 202}]] $\endgroup$
    – Sixty
    Nov 23, 2018 at 16:24
  • $\begingroup$ Anyone know how to make this work? I see the same thing that the ByteArray passing doesn't change that it still "fails". There must be a checksum or something in addition to the encrypted data that is failing on the decryption. $\endgroup$
    – Mark R
    Jul 21, 2019 at 7:18

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