PureBasic

AES-GCM Encryption / Decryption

See more Encryption Examples

Demonstrates AES-GCM encryption. Afterwards, the encrypted bytes, the authentication tag, and the IV are concatenated into one byte array and encoded to base64. For decryption, we decode the base64, extract the IV, authentication tag, and encrypted bytes, and then perform AES-GCM decryption. PureBasic

IncludeFile "CkCrypt2.pb"
IncludeFile "CkBinData.pb"

Procedure ChilkatExample()

    success.i = 0

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

    crypt.i = CkCrypt2::ckCreate()
    If crypt.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkCrypt2::setCkCryptAlgorithm(crypt, "aes")
    CkCrypt2::setCkCipherMode(crypt, "gcm")
    CkCrypt2::setCkKeyLength(crypt, 256)

    K.s = "000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F"
    IV.s = "000102030405060708090A0B0C0D0E0F"
    AAD.s = "feedfacedeadbeeffeedfacedeadbeefabaddad2"
    PT.s = "This is the text to be AES-GCM encrypted."

    CkCrypt2::ckSetEncodedIV(crypt,IV,"hex")
    CkCrypt2::ckSetEncodedKey(crypt,K,"hex")

    success = CkCrypt2::ckSetEncodedAad(crypt,AAD,"hex")

    ; Return the encrypted bytes as base64
    CkCrypt2::setCkEncodingMode(crypt, "base64")
    CkCrypt2::setCkCharset(crypt, "utf-8")
    cipherText.s = CkCrypt2::ckEncryptStringENC(crypt,PT)
    If CkCrypt2::ckLastMethodSuccess(crypt) <> 1
        Debug CkCrypt2::ckLastErrorText(crypt)
        CkCrypt2::ckDispose(crypt)
        ProcedureReturn
    EndIf

    ; Get the GCM authenticated tag computed when encrypting.
    authTag.s = CkCrypt2::ckGetEncodedAuthTag(crypt,"base64")

    Debug "Cipher Text: " + cipherText
    Debug "Auth Tag: " + authTag

    ; Let's send the IV, CipherText, and AuthTag to the decrypting party.
    ; We'll send them concatenated like this: [IV || Ciphertext || AuthTag]
    ; In base64 format.
    bdEncrypted.i = CkBinData::ckCreate()
    If bdEncrypted.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkBinData::ckAppendEncoded(bdEncrypted,IV,"hex")
    CkBinData::ckAppendEncoded(bdEncrypted,cipherText,"base64")
    CkBinData::ckAppendEncoded(bdEncrypted,authTag,"base64")

    concatenatedGcmOutput.s = CkBinData::ckGetEncoded(bdEncrypted,"base64")
    Debug "Concatenated GCM Output: " + concatenatedGcmOutput

    ; Sample output so far:

    ; -------------------------------------------------------------------------------------
    ; Now let's GCM decrypt...
    ; -------------------------------------------------------------------------------------

    decrypt.i = CkCrypt2::ckCreate()
    If decrypt.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; The values shared and agreed upon by both sides beforehand are: algorithm, cipher mode, secret key, and AAD.
    ; Sometimes the IV can be a value already known and agreed upon, but in this case the encryptor sends the IV to the decryptor.
    CkCrypt2::setCkCryptAlgorithm(decrypt, "aes")
    CkCrypt2::setCkCipherMode(decrypt, "gcm")
    CkCrypt2::setCkKeyLength(decrypt, 256)
    CkCrypt2::ckSetEncodedKey(decrypt,K,"hex")
    CkCrypt2::ckSetEncodedAad(decrypt,AAD,"hex")

    bdFromEncryptor.i = CkBinData::ckCreate()
    If bdFromEncryptor.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkBinData::ckAppendEncoded(bdFromEncryptor,concatenatedGcmOutput,"base64")

    sz.i = CkBinData::ckNumBytes(bdFromEncryptor)

    ; Extract the parts.
    extractedIV.s = CkBinData::ckGetEncodedChunk(bdFromEncryptor,0,16,"hex")
    extractedCipherText.s = CkBinData::ckGetEncodedChunk(bdFromEncryptor,16,sz - 32,"base64")
    expectedAuthTag.s = CkBinData::ckGetEncodedChunk(bdFromEncryptor,sz - 16,16,"base64")

    ; Before GCM decrypting, we must set the authenticated tag to the value that is expected.
    ; The decryption will fail if the resulting authenticated tag is not equal to the expected result.
    success = CkCrypt2::ckSetEncodedAuthTag(decrypt,expectedAuthTag,"base64")

    ; Also set the IV.
    CkCrypt2::ckSetEncodedIV(decrypt,extractedIV,"hex")

    ; Decrypt..
    CkCrypt2::setCkEncodingMode(decrypt, "base64")
    CkCrypt2::setCkCharset(decrypt, "utf-8")
    decryptedText.s = CkCrypt2::ckDecryptStringENC(decrypt,extractedCipherText)
    If CkCrypt2::ckLastMethodSuccess(decrypt) <> 1
        ; Failed.  The resultant authenticated tag did not equal the expected authentication tag.
        Debug CkCrypt2::ckLastErrorText(decrypt)
        CkCrypt2::ckDispose(crypt)
        CkBinData::ckDispose(bdEncrypted)
        CkCrypt2::ckDispose(decrypt)
        CkBinData::ckDispose(bdFromEncryptor)
        ProcedureReturn
    EndIf

    Debug "Decrypted: " + decryptedText

    ; Sample output:

    ; Cipher Text: cYspSW4GuSj0Msho4OgZZ0AwspDEpTF5Br8NlA+qT3f+g3nQo+xalmU=
    ; Auth Tag: z/N82vdj/ZsM0WnHNCnPPw==
    ; Concatenated GCM Output: AAECAwQFBgcICQoLDA0OD3GLKUluBrko9DLIaODoGWdAMLKQxKUxeQa/DZQPqk93/oN50KPsWpZlz/N82vdj/ZsM0WnHNCnPPw==
    ; Decrypted: This is the text to be AES-GCM encrypted.


    CkCrypt2::ckDispose(crypt)
    CkBinData::ckDispose(bdEncrypted)
    CkCrypt2::ckDispose(decrypt)
    CkBinData::ckDispose(bdFromEncryptor)


    ProcedureReturn
EndProcedure