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iPXE
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An AES lookup table. More...
Data Fields | |
| union aes_table_entry | entry [256] |
| Table entries, indexed by S(N) More... | |
An AES lookup table.
This represents the products (in the Galois field GF(2^8)) of a constant eight-byte vector multiplier with all possible 256 scalar multiplicands.
The entries are indexed by the AES [Inv]SubBytes S-box output values (denoted S(N)). This allows for the result of multiplying any single column of the [Inv]MixColumns matrix by S(N) to be obtained simply by extracting the relevant four-byte subset from the Nth table entry. For example:
Input byte (N): 0x3a SubBytes output S(N): 0x80 MixColumns column[1]: { 3, 2, 1, 1 } Vector multiplier: { 1, 1, 1, 3, 2, 1, 1, 3 } Table entry[0x3a]: { 0x80, 0x80, 0x80, 0x9b, 0x1b, 0x80, 0x80, 0x9b } Product: { 0x9b, 0x1b, 0x80, 0x80 }
Since the first byte of the eight-byte vector multiplier is always chosen to be 1, the value of S(N) may be lookup up by extracting the first byte of the Nth table entry.
| union aes_table_entry aes_table::entry[256] |
Table entries, indexed by S(N)
Definition at line 142 of file aes.c.
Referenced by aes_final(), aes_generate(), aes_key_sbox(), and aes_setkey().
1.8.15