CryptoSys API Library Manual

AES128_FileHex

Encrypts or decrypts a file using a specified mode. The key and initialization vector are passed as hexadecimal strings.

VB6/VBA Syntax

Public Declare Function AES128_FileHex Lib "diCryptoSys.dll" (ByVal strFileOut As String, ByVal strFileIn As String, ByVal strHexKey As String, ByVal bEncrypt As Boolean, ByVal strMode As String, ByVal strHexIV As String) As Long

nRet = AES128_FileHex(strFileOut, strFileIn, strHexKey, bEncrypt, strMode, strHexIV)

Parameters

strFileOut
[in] String with the full path name of the output file to be created.
strFileIn
[in] String with the full path name of the input file to be processed.
strHexKey
[in] String containing the key in hexadecimal.
bEncrypt
[in] Boolean direction flag: set as True to encrypt or False to decrypt.
strMode
[in] String 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.
strHexIV
[in] String containing the initialization vector (IV) in hexadecimal.

C/C++ Syntax

long _stdcall AES128_FileHex(const char *lpszFileOut, const char *lpszFileIn, const char *lpszKey, int bEncrypt, const char *lpszMode, const char *lpszIV);

Returns (VB6/C)

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

.NET Equivalent

Aes128.FileEncrypt Method (String, String, String, Mode, String)
Aes128.FileDecrypt Method (String, String, String, Mode, String)

Remarks

The key string strHexKey must be exactly 32 hexadecimal characters long (i.e. representing exactly 16 bytes/128 bits). The initialization vector strHexIV must be exactly 32 hexadecimal characters long (i.e. representing exactly the block size of 16 bytes), except for ECB mode, where it is ignored (use ""). The output file strFileOut will be overwritten without warning. If there is an error [new in version 3.3], the output file will not exist. The input and output filepaths must not be the same. In ECB and CBC modes, a padding string will be added or assumed according to the method outlined in Section 6.3 of [CMS], which is the same as the padding method in [PKCS7] and [PKCS5].

Note that even though the parameters are in hexadecimal-encoded form, the encrypted file is still binary.

Example

This example will encrypt the file "bigfile.dat" in CBC mode using the 128-bit key 0xfedcba9876543210fedcba9876543210 and initialization vector 0x0123456789abcdef0123456789abcdef. The output file "bigfile.cbc" will be created or overwritten.

    Dim nRet As Long
    nRet = AES128_FileHex("bigfile.cbc", "bigfile.dat", _
        "fedcba9876543210fedcba9876543210", _
        ENCRYPT, "CBC", "0123456789abcdef0123456789abcdef")
    If nRet <> 0 Then
        Debug.Print "AES128_FileHex failed: " & apiErrorLookup(nRet)
    Else
        Debug.Print "AES128_FileHex encrypted file OK"
    End If

See Also

AES128_File

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