RE: Decryption using private key from cert store failing with err

From: Rhett Gong [MSFT] (v-raygon_at_online.microsoft.com)
Date: 02/24/05 

Date: Thu, 24 Feb 2005 02:43:08 GMT

>call taking 117 bytes as input and generating 128 bytes as output. What
are
>the extra 11 bytes? They cannot just be padding, it appears to us that
they
>contain information that is used by the cryptdecrypt call
Yes, you are right. In Windows 2000 and later, the encryption uses PKCS #1
Type 2 padding. On decryption, this padding is verified. The length of
plaintext data that can be encrypted with a call to CryptEncrypt with an
RSA key is the length of the key modulus minus eleven bytes. The eleven
bytes is the chosen minimum for PKCS #1 padding. The ciphertext is returned
in little-endian format.

Thanks,
Rhett Gong [MSFT]
Microsoft Online Partner Support
Get Secure! - www.microsoft.com/security

This posting is provided "AS IS" with no warranties and confers no rights.

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