Xbase++

Decrypt 256-bit AES GCM Produced by Something Unknown

See more Encryption Examples

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

LOCAL nSuccess
LOCAL cKeyBase64
LOCAL cIvBase64Url
LOCAL cCipherBase64Url
LOCAL oCrypt
LOCAL oBdEncrypted
LOCAL oBdAuthTag
LOCAL nNumBytes
LOCAL cAuthTagHex
LOCAL cOriginalText

nSuccess := 0

//  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): 
cKeyBase64 := "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

//  IV (Base64Url):
cIvBase64Url := "xrvaINMLqotAbWRK"

//  ciphertext (base64url):
cCipherBase64Url := "RtGNAS-zQOxSB8W0HfqJjCoyt9KgImW_l-HjVC40hOOl-RNfRF3hzDIT1kvFVF8i_KX9XmqAftb6lyq-jLCEc_MSgqt3q1ixv3Ez4SbS3G5e3qGzLwxIMi2sCt00aDNwK2ipsJ4aw8s7ePPnl4oY-y1st9rwCWR0rrgEZwS9jmS4uJWGPn9K3jbKRnMslznDbtFLNJctMVXBTP-cv47JelxLCBOQSlK29rMuEFrhHR_VQrPq6gtZaBVSXZSYT0XOklp7nu9mVhrMCRtBCC5oiu5MPE5JYx4ANo3hUY7_NyQl2bpn9GfRXrdvqRGE-gy2upj-cDkm0t_tV8xmYge9DBQTH3B_4BGl2qTk_o-m7pEmKkS8XSdQhGcuFlykqrkE8SzB5I8esfzWOM0pwxbz0H_VaylKYHY="

oCrypt := CreateObject("Chilkat.Crypt2")

oCrypt:CryptAlgorithm := "aes"
oCrypt:CipherMode := "gcm"
oCrypt:KeyLength := 256

nSuccess := oCrypt:SetEncodedAad("random", "ascii")
oCrypt:SetEncodedKey(cKeyBase64, "base64")
oCrypt:SetEncodedIV(cIvBase64Url, "base64url")

//  The cipher text contains the 16-byte auth tag at the end.
//  get it separately..
oBdEncrypted := CreateObject("Chilkat.BinData")
oBdAuthTag := CreateObject("Chilkat.BinData")
nSuccess := oBdEncrypted:AppendEncoded(cCipherBase64Url, "base64url")

nNumBytes := oBdEncrypted:NumBytes
cAuthTagHex := oBdEncrypted:GetEncodedChunk(nNumBytes - 16, 16, "hex")

? "Auth tag in hex: " + cAuthTagHex

nSuccess := oBdAuthTag:AppendEncoded(cAuthTagHex, "hex")
oBdEncrypted:RemoveChunk(nNumBytes - 16, 16)

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

//  Decrypt
oCrypt:EncodingMode := "base64"
cOriginalText := oCrypt:DecryptStringENC(oBdEncrypted:GetEncoded("base64"))
IF (oCrypt:LastMethodSuccess == 0)
    ? oCrypt:LastErrorText
ELSE
    ? cOriginalText
    ? "Success."
ENDIF

//  Decrypted text

oCrypt:destroy()
oBdEncrypted:destroy()
oBdAuthTag:destroy()