5812-DS01-R datasheet(78/84 Pages) BOARDCOM

78 / 84 page

BCM5812

Advance Data Sheet

3/11/03

B roa dcom Co rpo rat ion

Page 70

Modular Arithmetic Operation Restrictions

Document

5812-DS01-405-R

INCORRECT DATA SIZE FOR ENCRYPTION

Whenever 3DES or AES is enabled, the length of input data to be encrypted or decrypted must be a multiple of the block

size, which is eight bytes for 3DES and sixteen bytes for AES. The BCM5812 calculates this length as the packet length from

the command context minus the number of bytes (specified in 32-bit words) in the offset field in the command context.

WRITING TO THE MCR REGISTER WITH PCI MASTER MODE DISABLED

Doing so causes the BCM5812 control microcode to start processing, waiting for a PCI master mode access that never

begins.

MODULAR ARITHMETIC OPERATION RESTRICTIONS

In modular exponentiation, the exponent length must be less than modulus length. In all modular arithmetic operations, the

modulus cannot be less than 16 bits.

In all modular arithmetic operations other than remainder, the arguments must be less than the modulus. In remainder, the

input parameter size must be equal to modulus parameter size. Thus, the input argument must be between the modulus and

the maximum parameter size.

CHAINING OPERATION DEPENDENCIES

BCM5812 can perform chaining operations (The output of the first operation feeds as the input to the second operation within

the same MCR) for the most frequent SSL/TLS operations. However, it has limitation how the chaining operations can be

done in the other SSL/TLS operations.

SSL-MAC OR TLS-HMAC FOLLOWED BY ARCFOUR

Figure 12 on page 14 shows the structure of SSL or TLS protocol records. For outgoing SSL or TLS record layer processing,

which typically requires computing the authentication code over the clear text followed by encryption of the data with the

authentication code appended, the BCM5812 allows authentication and encryption to be performed in back to back packet

descriptors in the same MCR.

In other words, it is safe to use the SSL-MAC or TLS-HMAC hash output as the data input to ARCFOUR. The authentication

code may need its own fragment chain entry to assure compliance with alignment of the authentication code on a 32-bit

boundary (see “Alignment Restrictions” on page 71 below).

ARCFOUR OR 3DES FOLLOWED BY SSL-MAC OR TLS-HMAC

Incoming SSL or TLS record layer processing typically requires decryption followed by computing the authentication code

over the clear text. For the BCM5812, decryption followed by authentication of the decrypted data can be performed in back

to back packet descriptors in the same MCR. In other words, it is safe to have the ARCFOUR or 3DES data output as input

to the SSL-MAC or TLS-HMAC.

5812-DS01-R 数据表(PDF) 78 Page - Broadcom Corporation.

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