(Lianja) Decrypt 256-bit AES GCM Produced by Something Unknown

Demonstrates how to decrypt something produced elsewhere (unknown) with 256-bit AES GCM.

Chilkat Lianja Extension Download Chilkat Lianja Extension

// This example assumes the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// We have the following to decrypt:

// Key (Base64): 
lcKeyBase64 = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

// IV (Base64Url):
lcIvBase64Url = "xrvaINMLqotAbWRK"

// ciphertext (base64url):
lcCipherBase64Url = "RtGNAS-zQOxSB8W0HfqJjCoyt9KgImW_l-HjVC40hOOl-RNfRF3hzDIT1kvFVF8i_KX9XmqAftb6lyq-jLCEc_MSgqt3q1ixv3Ez4SbS3G5e3qGzLwxIMi2sCt00aDNwK2ipsJ4aw8s7ePPnl4oY-y1st9rwCWR0rrgEZwS9jmS4uJWGPn9K3jbKRnMslznDbtFLNJctMVXBTP-cv47JelxLCBOQSlK29rMuEFrhHR_VQrPq6gtZaBVSXZSYT0XOklp7nu9mVhrMCRtBCC5oiu5MPE5JYx4ANo3hUY7_NyQl2bpn9GfRXrdvqRGE-gy2upj-cDkm0t_tV8xmYge9DBQTH3B_4BGl2qTk_o-m7pEmKkS8XSdQhGcuFlykqrkE8SzB5I8esfzWOM0pwxbz0H_VaylKYHY="

loCrypt = createobject("CkCrypt2")

loCrypt.CryptAlgorithm = "aes"
loCrypt.CipherMode = "gcm"
loCrypt.KeyLength = 256

llSuccess = loCrypt.SetEncodedAad("random","ascii")
loCrypt.SetEncodedKey(lcKeyBase64,"base64")
loCrypt.SetEncodedIV(lcIvBase64Url,"base64url")

// The cipher text contains the 16-byte auth tag at the end.
// get it separately..
loBdEncrypted = createobject("CkBinData")
loBdAuthTag = createobject("CkBinData")
llSuccess = loBdEncrypted.AppendEncoded(lcCipherBase64Url,"base64url")

lnNumBytes = loBdEncrypted.NumBytes
lcAuthTagHex = loBdEncrypted.GetEncodedChunk(lnNumBytes - 16,16,"hex")

? "Auth tag in hex: " + lcAuthTagHex

llSuccess = loBdAuthTag.AppendEncoded(lcAuthTagHex,"hex")
loBdEncrypted.RemoveChunk(lnNumBytes - 16,16)

// Use this special value to tell Chilkat to ignore the auth tag.
llSuccess = loCrypt.SetEncodedAuthTag("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF","hex")

// Decrypt
loCrypt.EncodingMode = "base64"
lcOriginalText = loCrypt.DecryptStringENC(loBdEncrypted.GetEncoded("base64"))
if (loCrypt.LastMethodSuccess = .F.) then
    ? loCrypt.LastErrorText
else
    ? lcOriginalText
    ? "Success."
endif

// Decrypted text


release loCrypt
release loBdEncrypted
release loBdAuthTag