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

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

Chilkat Go Downloads Go Package for Windows, MacOS, Linux, Alpine Linux, Solaris

    // 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): 
    keyBase64 := "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

    // IV (Base64Url):
    ivBase64Url := "xrvaINMLqotAbWRK"

    // ciphertext (base64url):
    cipherBase64Url := "RtGNAS-zQOxSB8W0HfqJjCoyt9KgImW_l-HjVC40hOOl-RNfRF3hzDIT1kvFVF8i_KX9XmqAftb6lyq-jLCEc_MSgqt3q1ixv3Ez4SbS3G5e3qGzLwxIMi2sCt00aDNwK2ipsJ4aw8s7ePPnl4oY-y1st9rwCWR0rrgEZwS9jmS4uJWGPn9K3jbKRnMslznDbtFLNJctMVXBTP-cv47JelxLCBOQSlK29rMuEFrhHR_VQrPq6gtZaBVSXZSYT0XOklp7nu9mVhrMCRtBCC5oiu5MPE5JYx4ANo3hUY7_NyQl2bpn9GfRXrdvqRGE-gy2upj-cDkm0t_tV8xmYge9DBQTH3B_4BGl2qTk_o-m7pEmKkS8XSdQhGcuFlykqrkE8SzB5I8esfzWOM0pwxbz0H_VaylKYHY="

    crypt := chilkat.NewCrypt2()

    crypt.SetCryptAlgorithm("aes")
    crypt.SetCipherMode("gcm")
    crypt.SetKeyLength(256)

    success := crypt.SetEncodedAad("random","ascii")
    crypt.SetEncodedKey(keyBase64,"base64")
    crypt.SetEncodedIV(ivBase64Url,"base64url")

    // The cipher text contains the 16-byte auth tag at the end.
    // get it separately..
    bdEncrypted := chilkat.NewBinData()
    bdAuthTag := chilkat.NewBinData()
    success = bdEncrypted.AppendEncoded(cipherBase64Url,"base64url")

    numBytes := bdEncrypted.NumBytes()
    authTagHex := bdEncrypted.GetEncodedChunk(numBytes - 16,16,"hex")

    fmt.Println("Auth tag in hex: ", *authTagHex)

    success = bdAuthTag.AppendEncoded(*authTagHex,"hex")
    bdEncrypted.RemoveChunk(numBytes - 16,16)

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

    // Decrypt
    crypt.SetEncodingMode("base64")
    originalText := crypt.DecryptStringENC(*bdEncrypted.GetEncoded("base64"))
    if crypt.LastMethodSuccess() == false {
        fmt.Println(crypt.LastErrorText())
    } else {
        fmt.Println(*originalText)
        fmt.Println("Success.")
    }

    // Decrypted text

    crypt.DisposeCrypt2()
    bdEncrypted.DisposeBinData()
    bdAuthTag.DisposeBinData()