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iPXE
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A single AES lookup table entry. More...
Data Fields | |
| uint8_t | byte [8] |
| Viewed as an array of bytes. More... | |
A single AES lookup table entry.
This represents the product (in the Galois field GF(2^8)) of an eight-byte vector multiplier with a single scalar multiplicand.
The vector multipliers used for AES will be {1,1,1,3,2,1,1,3} for MixColumns and {1,9,13,11,14,9,13,11} for InvMixColumns. This allows for the result of multiplying any single column of the [Inv]MixColumns matrix by a scalar value to be obtained simply by extracting the relevant four-byte subset from the lookup table entry.
For example, to find the result of multiplying the second column of the MixColumns matrix by the scalar value 0x80:
MixColumns column[0]: { 2, 1, 1, 3 } MixColumns column[1]: { 3, 2, 1, 1 } MixColumns column[2]: { 1, 3, 2, 1 } MixColumns column[3]: { 1, 1, 3, 2 } Vector multiplier: { 1, 1, 1, 3, 2, 1, 1, 3 } Scalar multiplicand: 0x80 Lookup table entry: { 0x80, 0x80, 0x80, 0x9b, 0x1b, 0x80, 0x80, 0x9b }
The second column of the MixColumns matrix is {3,2,1,1}. The product of this column with the scalar value 0x80 can be obtained by extracting the relevant four-byte subset of the lookup table entry:
MixColumns column[1]: { 3, 2, 1, 1 } Vector multiplier: { 1, 1, 1, 3, 2, 1, 1, 3 } Lookup table entry: { 0x80, 0x80, 0x80, 0x9b, 0x1b, 0x80, 0x80, 0x9b } Product: { 0x9b, 0x1b, 0x80, 0x80 }
The column lookups require only seven bytes of the eight-byte entry: the remaining (first) byte is used to hold the scalar multiplicand itself (i.e. the first byte of the vector multiplier is always chosen to be 1).
| uint8_t aes_table_entry::byte[8] |
Viewed as an array of bytes.
Definition at line 114 of file aes.c.
Referenced by aes_entry_column(), aes_final(), aes_generate(), aes_invmixcolumns_entry(), aes_key_sbox(), aes_mixcolumns_entry(), and aes_setkey().
1.8.15