diff options
| -rw-r--r-- | lib/aes.go | 97 |
1 files changed, 97 insertions, 0 deletions
diff --git a/lib/aes.go b/lib/aes.go new file mode 100644 index 0000000..ecc7479 --- /dev/null +++ b/lib/aes.go @@ -0,0 +1,97 @@ +// Copyright © 2020 rsiddharth <s@ricketyspace.net> +// SPDX-License-Identifier: ISC + +package lib + +// Returns a key schedule (44 bytes, 11 4-byte words) given a key 'k' +// (16 bytes, 4 4-byte words). +func KeyExpansion(k []byte) [][]byte { + ks := make([][]byte, 44) // key schedule + nk := 4 + nb := 4 + nr := 10 + + // Generate first 4 (Nk) words of the key schedule from the + // key 'k' + for i := 0; i < nk; i++ { + ks[i] = make([]byte, 4) + + ks[i][0] = k[(4*i)+0] + ks[i][1] = k[(4*i)+1] + ks[i][2] = k[(4*i)+2] + ks[i][3] = k[(4*i)+3] + } + + // Generate the rest of the key schedule. + for i := 4; i < (nb * (nr + 1)); i++ { + tmp := make([]byte, 4) + copy(tmp, ks[i-1]) + + if i%nk == 0 { + tmp = FixedXORBytes(SubWord(RotWord(tmp)), rcon[i/nk]) + } + ks[i] = make([]byte, 4) + ks[i] = FixedXORBytes(ks[i-nk], tmp) + } + + return ks +} + +// Performs a cyclic permutation to the left on the 4-byte word. +func RotWord(w []byte) []byte { + for i := 1; i < 4; i++ { + t := w[i-1] + w[i-1] = w[i] + w[i] = t + } + return w +} + +// Performs S-Box transformation on the 4-byte word. +func SubWord(w []byte) []byte { + sw := make([]byte, 4) + + for i := 0; i < 4; i++ { + r := w[i] >> 4 + c := w[i] & 0x0f + + sw[i] = sbox[r][c] + } + return sw +} + +// Generated using https://github.com/mvaneerde/blog/blob/061f/rijndael/s-box.pl +var sbox [16][16]byte = [16][16]byte{ + {0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76}, + {0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0}, + {0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15}, + {0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75}, + {0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84}, + {0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf}, + {0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8}, + {0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2}, + {0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73}, + {0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb}, + {0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79}, + {0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08}, + {0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a}, + {0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e}, + {0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf}, + {0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16}, +} + +// Round constants for 1 <= i <= 10 +// From https://en.wikipedia.org/wiki/AES_key_schedule#Rcon +var rcon [11][]byte = [11][]byte{ + {0x00, 0x00, 0x00, 0x00}, // i = 0; dummy + {0x01, 0x00, 0x00, 0x00}, + {0x02, 0x00, 0x00, 0x00}, + {0x04, 0x00, 0x00, 0x00}, + {0x08, 0x00, 0x00, 0x00}, + {0x10, 0x00, 0x00, 0x00}, + {0x20, 0x00, 0x00, 0x00}, + {0x40, 0x00, 0x00, 0x00}, + {0x80, 0x00, 0x00, 0x00}, + {0x1b, 0x00, 0x00, 0x00}, + {0x36, 0x00, 0x00, 0x00}, +} |