AES256_HexMode

Encrypts or decrypts data represented as a hexadecimal string using a specified mode. The key and initialization vector are represented as a hexadecimal string.

VBA/VB6 Syntax

AES256_HexMode(strOutput, strInput, strHexKey, bEncrypt, strMode, strHexIV)

C/C++ Syntax

Parameters

szOutput

[out] of sufficient length to receive the output.

szInput

[in] containing the input data in hexadecimal.

szKey

[in] containing the key in hexadecimal.

fEncrypt

[in] direction flag: set as ENCRYPT (True) to encrypt or DECRYPT (False) to decrypt.

szMode

[in] specifying the confidentiality mode:
"ECB" for Electronic Codebook mode,
"CBC" for Cipher Block Chaining mode,
"CFB" for 128-bit Cipher Feedback mode,
"OFB" for Output Feedback mode, or
"CTR" for Counter mode.

szIV

[in] containing the initialization vector (IV) in hexadecimal.

Returns (VBA/C)

If successful, the return value is 0; otherwise it returns a non-zero error code.

.NET Equivalent

Aes256.Encrypt Method (String, String, Mode, String)
Aes256.Decrypt Method (String, String, Mode, String)

Remarks

The length of the input string szInput must be a multiple of 32 hex characters long (i.e. representing a multiple of the block size of 16 bytes). The key string szHexKey must be exactly 64 hex characters long (i.e. representing exactly 32 bytes/256 bits). The initialization vector szHexIV must be exactly 32 hex characters long (i.e. representing exactly the block size of 16 bytes), except for ECB mode, where it is ignored (use ""). The output string szOutput must be set up with at least the same number of characters as the input string before calling. The variables szOutput and szInput should be different. Valid hexadecimal characters are [0-9A-Fa-f].

Example

The examples are from RFC 3602 The AES-CBC Cipher Algorithm and Its Use with IPsec

    Dim nRet As Long
    Dim strOutput As String
    Dim strInput As String
    Dim strHexKey As String
    Dim sPlain As String
    Dim sCipher As String
    Dim strHexIV As String
    
' Encrypting 64 bytes (4 blocks) using AES-CBC with 256-bit key
    
    strHexKey = "56e47a38c5598974bc46903dba29034906a9214036b8a15b512e03d534120006"
    strHexIV = "8ce82eefbea0da3c44699ed7db51b7d9"
    sPlain = "a0a1a2a3a4a5a6a7a8a9aaabacadaeaf" _
        & "b0b1b2b3b4b5b6b7b8b9babbbcbdbebf" _
        & "c0c1c2c3c4c5c6c7c8c9cacbcccdcecf" _
        & "d0d1d2d3d4d5d6d7d8d9dadbdcdddedf"
    sCipher = "28409A2982BD2CF7CE343A7D43F6927F" _
        & "DB9EC532BBA569EEC92E57A209C4FDBA" _
        & "59ADBA05A5C854694DDC9F7991C01634" _
        & "E72BEB4FE0236CB3B119A463891E346F"
        
    strInput = sPlain
    ' Set strOutput to be same length as strInput
    strOutput = String(Len(strInput), " ")
    
    Debug.Print "KY=" & strHexKey
    Debug.Print "IV=" & strHexIV
    Debug.Print "PT=" & strInput
    ' Encrypt in one-off process
    nRet = AES256_HexMode(strOutput, strInput, strHexKey, ENCRYPT, "CBC", strHexIV)
    Debug.Print "CT=" & strOutput; nRet
    Debug.Print "OK=" & sCipher
    Debug.Assert (strOutput = sCipher)

    ' Decrypt to check
    strInput = strOutput
    nRet = AES256_HexMode(strOutput, strInput, strHexKey, DECRYPT, "CBC", strHexIV)
    Debug.Print "P'=" & strOutput; nRet
    Debug.Print "OK=" & sPlain
    Debug.Assert (strOutput = sPlain)

This should result in output as follows:

KY=56e47a38c5598974bc46903dba29034906a9214036b8a15b512e03d534120006
IV=8ce82eefbea0da3c44699ed7db51b7d9
PT=a0a1a2a3a4a5a6a7a8a9aaabacadaeafb0b1b2b3b4b5b6b7b8b9babbbcbdbebf
c0c1c2c3c4c5c6c7c8c9cacbcccdcecfd0d1d2d3d4d5d6d7d8d9dadbdcdddedf
CT=28409A2982BD2CF7CE343A7D43F6927FDB9EC532BBA569EEC92E57A209C4FDBA
59ADBA05A5C854694DDC9F7991C01634E72BEB4FE0236CB3B119A463891E346F 0 
OK=28409A2982BD2CF7CE343A7D43F6927FDB9EC532BBA569EEC92E57A209C4FDBA
59ADBA05A5C854694DDC9F7991C01634E72BEB4FE0236CB3B119A463891E346F
P'=A0A1A2A3A4A5A6A7A8A9AAABACADAEAFB0B1B2B3B4B5B6B7B8B9BABBBCBDBEBF
C0C1C2C3C4C5C6C7C8C9CACBCCCDCECFD0D1D2D3D4D5D6D7D8D9DADBDCDDDEDF 0 
OK=a0a1a2a3a4a5a6a7a8a9aaabacadaeafb0b1b2b3b4b5b6b7b8b9babbbcbdbebf
c0c1c2c3c4c5c6c7c8c9cacbcccdcecfd0d1d2d3d4d5d6d7d8d9dadbdcdddedf

See Also

AES256_Hex

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