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PRB: Cannot Decrypt Data Using Data Encryption Standard (DES) Key Across Windows Platforms


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Symptoms

Data that is encrypted using the data encryption standard (DES) key in Microsoft Windows XP or later versions cannot be decrypted in pre-Windows XP operating systems (such as Microsoft Windows 2000 or Windows NT 4.0).

Likewise, data that is encrypted using the DES key in these earlier versions of Windows cannot be decrypted in Windows XP or later.

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Cause

In Windows XP and later versions, DES algorithm implementation always uses the full key length for DES algorithms, regardless of the key length specified by the application.

The key length is specified in the upper 16 bits of the dwFlags parameter in the CryptDeriveKey() function or the CryptGenKey() function calls.

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Resolution

Microsoft Windows XP and Later Versions

In Windows XP and later versions, the DES session key always uses the full key length as follows:
CALG_DES - 64 bits
CALG_3DES_112 - 128 bits
CALG_3DES - 192 bits
					

Versions Earlier than Windows XP

On platforms earlier than Windows XP (Microsoft Windows 2000, Windows NT 4.0, Windows 95, Windows 98, and Windows Millennium Edition), if the application does not specify a key length in the upper 16 bits of dwFlags, the DES session key size is as follows:
CALG_DES - 64 bits
CALG_3DES_112 - 128 bits
CALG_3DES - 192 bits
					
On platforms earlier than Windows XP, CryptDeriveKey() and CryptGenKey() calls accept the following key size without parity bits for DES algorithms:
CALG_DES - 64 - 8 bits (Parity) = 56 bits
CALG_3DES_112 - 128 - 16 bits (Parity) = 112 bits
CALG_3DES - 192 - 24 bits (Parity) = 168 bits
					
If the application specifies this key size without the parity bits in the upper 16 bits of dwFlags, the decryption does not succeed between Windows XP and pre-Windows XP operating systems. Specifically, CryptDecrypt() does not succeed and generates the 0x80090005 (NTE_BAD_DATA) error.

To encrypt and decrypt across Windows platforms, explicitly specify the key size that corresponds to the Windows XP implementation in either the CryptDeriveKey() function or the CryptGenKey() function (or in both functions). You can specify the Windows XP key sizes for DES algorithms if you have the high encryption pack installed on the earlier versions of the operating system.

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Status

This behavior is by design.

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More information

The encryption and decryption for DES family algorithms works fine across Windows platforms if the application uses the default key size (that is, if the application does not specify a key length in the upper 16 bits of the dwFlags parameter in CryptGenKey() or CryptDeriveKey() calls).

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Keywords: kbapi, kbcrypt, kbkernbase, kbpending, kbprb, kbsecurity, KB331367

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Article Info
Article ID : 331367
Revision : 8
Created on : 1/5/2007
Published on : 1/5/2007
Exists online : False
Views : 131