(Classic ASP) Hashing Encoded Data

This example explains how it's important to know exactly what bytes are getting hashed when working with encoded data, such as hex, base64, etc.

Chilkat ActiveX Downloads

ActiveX for 32-bit and 64-bit Windows

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

' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Crypt2")
set crypt = Server.CreateObject("Chilkat.Crypt2")

' Imagine we want to SHA-1 hash this A9133F6DC63E85BE0619763F8975CA076FF91B95CB6F121CD21C016143315E11B9ED4374F174B2CC
strToHash = "A9133F6DC63E85BE0619763F8975CA076FF91B95CB6F121CD21C016143315E11B9ED4374F174B2CC"

' The question is:  Do we want to hash the bytes 0xA9, 0x13, 0x3F...
' or do we want to literally hash each us-ascii byte:  'A', '9', '1', '3'.

' The results will obviously be different depending on what bytes are actually hashed.

' To hash the decoded bytes (i.e. 0xA9, 0x13, 0x3F...) we do this:

' "hex" is not an actual character encoding.  It's a special value to be used to tell Chilkat to hex decode
' the string and pass the decoded bytes to the hash algorithm...
crypt.Charset = "hex"
crypt.HashAlgorithm = "sha1"
' Get the hash result in lowercase hex
crypt.EncodingMode = "hex_lower"
hashValue = crypt.HashStringENC(strToHash)
Response.Write "<pre>" & Server.HTMLEncode( "hash of decoded hex bytes: " & hashValue) & "</pre>"

' The result is 7a4a2ba73811fab98b4baaee2df164cbdd0d8e8e

' This is how to hash the us-ascii byte values:
' The Charset property defines the byte representation of the string passed to the hash algorithm:
crypt.Charset = "us-ascii"
' The EncodingMode property defines the binary encoding (hex, base64, etc.) of the hash returned as an encoded string.
crypt.EncodingMode = "hex"
crypt.HashAlgorithm = "sha1"

hashValue = crypt.HashStringENC(strToHash)
Response.Write "<pre>" & Server.HTMLEncode( "hash of us-ascii bytes: " & hashValue) & "</pre>"

' The result is:  2A7500F88734F4B19C79852CA0FF3E1C561F31C8

' 

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