5812-DS00-R datasheet(18/84 Pages) BOARDCOM

18 / 84 page

BCM5812

Advance Data Sheet

3/11/03

B roa dcom Co rpo rat ion

Page 10

Cryptographic Operations

Document

5812-DS01-405-R

Figure 7: CBC Mode

If authentication is performed, it is done over the entire packet length. If encryption is performed (i.e., the direction in

Table 4 on page 7 is outbound), the packet is encrypted beginning at the offset, and then authentication is performed over

the entire packet length, including the ciphertext. If decryption is performed (i.e., the direction is inbound), authentication is

performed over the entire packet length, and then the packet is decrypted beginning at the offset.

Figure 8 on page 11 also shows the position of the IV in an IP packet that is ESP-encapsulated according to RFC 2405.

Figure 8 shows the byte order of the data as little-endian host CPU byte order. The BCM5812 can be configured to interpret

these network bytes in big-endian host CPU byte order (See “Endian Considerations” on page 42). For 3DES, the

initialization vector (IV) length is 8 bytes.

Figure 10 on page 12 shows the corresponding output buffer described using a list of output fragment chain entries.

If encryption or decryption is performed, data is written into successive fragment buffers according to each output fragment

chain entry’s output fragment length until the total of the encrypted or decrypted length (input packet length minus the offset)

is satisfied.

Note

•

Output fragment chain entries must be 32-bit aligned in host memory.

•

Output fragment buffers must be 32-bit aligned in host memory.

•

The total encrypted or decrypted length must be a multiple of the cipher block size (8 bytes for 3DES

and DES)

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