Microsoft Strong and Enhanced cryptographic service providers (CSP)
on Windows NT and Windows 2000 generate RC2 keys
that have the effective key length of 40 bits by default regardless
of the requested key length. Thus, the AspEncrypt methods
GenerateKey and GenerateKeyFromPassword with the last argument
(Key Size) set to 128 still generate 40-bit RC2 keys on Windows NT and 2000,
although the property Key.Length returns 128.
NOTE: The above statement is only true for RC2 keys. With
the algorithms RC4, DES, 3DES, and 3DES2, the effective key length
matches the requested key length on all platforms.
The cryptographic providers on Windows XP and 2003, on the other hand,
generate RC2 keys with the effective key length matching that
of Key.Length. As a result, 128-bit keys generated on
Windows NT/2000 and those generated on Windows 2003/XP
do not match (as their effective lengths are 40 and 128, respectively).
AspEncrypt 2.2 (released on September 16, 2003) provides
a workaround for this problem by offering a new property,
Key.EffectiveLength
which can be used to retrieve and specify the effective key length for RC2 keys.
On Windows XP/2003, to generate a key that matches
a 128-bit RC2 created on a Windows NT/2000 box, use the following code:
' Use SHA and RC2 by default
Set Key = Context.GenerateKeyFromPassword("pwd", , , 128)
Key.EffectiveLength = 40
Text = Key.DecryptText(Blob)
It is recommended that all your RC2-encrypted data be decrypted and then
re-encrypted using a key with the effective key length of 128, as follows:
Set Key = Context.GenerateKeyFromPassword("pwd", , , 128)
Key.EffectiveLength = 128
Set Blob = Key.EncryptText(...)
Upgrades to AspEncrypt 2.2 are absolutely free for registered users.
The new version can be downloaded at
www.aspencrypt.com/download.html.
