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IXP400 Software
Access-Layer Components: Security (IxCryptoAcc) API
April 2005 IXP400 Software Version 2.0 Programmer’s Guide
112 Document Number: 252539, Revision: 007
SSL client applications can make use of the ARC4 processing features by registering an
encryption-only or decryption-only crypto context and the IxCryptoAccXScaleWepPerform() or
IxCryptoAccNpeWepPerform() functions. SSL clients should supply a full 128-bit key to the API.
7.7.2 Cipher Modes
There are four cipher modes supported by the NPE:
• Electronic code book (ECB)
• Cipher block chaining (CBC)
• Counter Mode (CTR)
• Counter-Mode / CBC-MAC Protocol (CCMP)
7.7.2.1 Electronic Code Book (ECB)
The ECB mode for encryption and decryption is supported for DES, Triple DES and AES. ECB is
a direct application of the DES algorithm to encrypt and decrypt data.
When using the DES in ECB mode and any particular key, each input is mapped onto a unique
output in encryption and this output is mapped back onto the input in decryption. The DES is an
iterative, block, product-cipher system (that is, encryption algorithm). A product-cipher system
mixes transposition and substitution operations in an alternating manner.
7.7.2.2 Cipher Block Chaining (CBC)
The CBC mode for encryption and decryption is supported for DES, Triple DES, and AES. It
requires initialization vector (IV) of size 64-bit for DES and 128-bit for AES initialization vector
(IV).
7.7.2.3 Counter Mode (CTR)
The counter mode (CTR) is only applicable for AES. The counter block consists of the SPI (the
32-bit value used to distinguish among different SAs terminating at the same destination and using
the same IPSec protocol), IV, and a counter that is incremented per input block of plain text. The
same AES key is used for the entire encryption process.
The counter block is always constructed by the client.
7.7.2.4 Counter-Mode Encryption with CBC-MAC Authentication (CCM)
for CCMP in 802.11i
A protocol based on AES and Counter-Mode/CBC-MAC is being adopted for providing enhanced
security in wireless LAN networks. This protocol is called Counter-Mode/CBC-MAC Protocol
(CCMP). The standard defines the CCMP encapsulation/decapsulation processes, CCMP-MPDU
formats, CCMP-states and CCMP-procedures. This section provides CCMP-procedure details for
constructing CCM initial block (also called MIC-IV), MIC-Headers for performing CCMP MIC
computation and CCM-CTR mode IV construction for performing CCM-CTR mode encryption/
decryption.