SHA2_Hmac

Is a keyed-hash function that provides message authentication using the HMAC algorithm and the SHA-256 hash function.

VBA/VB6 Syntax

nRet = SHA2_Hmac(strDigest, abData(0), nDataLen, abKey(0), nKeyLen) ' Note the "(0)" after the byte array parameters

C/C++ Syntax

Parameters

szDigest

[out] variable of sufficient length to receive the message digest in hex format.

textBytes

[in] array containing the text of the message.

textLen

[in] containing the number of bytes in the array

lpKeyBytes

[in] array containing the key.

keyLen

[in] containing the number of bytes in the key

Returns (VBA/C)

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

.NET Equivalent

Sha256.Hmac Method (Byte[], Byte[])

Remarks

szDigest must be at least 64 (API_MAX_SHA2_CHARS) characters long (65 in a C program).

Example

This example reproduces the three test vectors from RFC 2014 using SHA-256 instead of MD5. Note that the results will be different from those given in RFC 2104 because a different hash function is used (RFC 2104 uses MD5).

    Dim nRet As Long
    Dim abData() As Byte
    Dim abKey() As Byte
    Dim i As Integer
    Dim nDataLen As Long, nKeyLen As Long
    Dim strDigest As String * 64

    ' Test No 1.
    ' Set key = 0x0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b
    ReDim abKey(15)
    For i = 0 To 15
        abKey(i) = &HB
    Next
    ' Convert string to byte array
    abData() = StrConv("Hi There", vbFromUnicode)
    nDataLen = UBound(abData) + 1
    ' Create HMAC digest
    nRet = SHA2_Hmac(strDigest, abData(0), nDataLen, abKey(0), 16)
    Debug.Print 1; nRet; strDigest

    ' Test No 2.
    abKey() = StrConv("Jefe", vbFromUnicode)
    nKeyLen = UBound(abKey) + 1
    abData() = StrConv("what do ya want for nothing?", vbFromUnicode)
    nDataLen = UBound(abData) + 1
    nRet = SHA2_Hmac(strDigest, abData(0), nDataLen, abKey(0), nKeyLen)
    Debug.Print 2; nRet; strDigest

    ' Test No 3.
    ReDim abKey(15)
    For i = 0 To 15
        abKey(i) = &HAA
    Next
    ReDim abData(49)
    For i = 0 To 49
        abData(i) = &HDD
    Next
    nRet = SHA2_Hmac(strDigest, abData(0), 50, abKey(0), 16)
    Debug.Print 3; nRet; strDigest

This should result in output as follows:

 1  0 492ce020fe2534a5789dc3848806c78f4f6711397f08e7e7a12ca5a4483c8aa6
 2  0 5bdcc146bf60754e6a042426089575c75a003f089d2739839dec58b964ec3843
 3  0 7dda3cc169743a6484649f94f0eda0f9f2ff496a9733fb796ed5adb40a44c3c1

See Also

SHA1_Hmac

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