diff options
| -rw-r--r-- | challenge/c18.go | 24 | ||||
| -rw-r--r-- | lib/aes.go | 23 |
2 files changed, 24 insertions, 23 deletions
diff --git a/challenge/c18.go b/challenge/c18.go index 00d1146..a84776e 100644 --- a/challenge/c18.go +++ b/challenge/c18.go @@ -11,31 +11,9 @@ import ( // Cryptopals #18 - Implement CTR, the stream cipher mode func C18() { - // Generates counter function for AES CTR mode. - genCTRFunc := func(nonce uint64) func() []byte { - ctr := uint64(0) // Counter - ff := uint64(0xFF) - cf := func() []byte { - cb := make([]byte, 16) // counter block - var i, j uint - // Put nonce in the first 8 bytes in cb in little endian format - for i = 0; i < 8; i++ { - n := nonce & (ff << (i * 8)) // Reset all except the i^th byte of the nonce - cb[i] = byte(n >> (i * 8)) // Retrieve i^th byte of the nonce - } - // Put counter in the next 8 bytes in cb in little endian format - for i, j = 8, 0; i < 16; i, j = i+1, j+1 { - n := ctr & (ff << (j * 8)) // Reset all except the j^th byte of the counter - cb[i] = byte(n >> (j * 8)) // Retrieve j^th byte of the counter - } - ctr += 1 // Increment counter by 1 - return cb - } - return cf - } cipher := lib.Base64ToBytes("L77na/nrFsKvynd6HzOoG7GHTLXsTVu9qvY/2syLXzhPweyyMTJULu/6/kXX0KSvoOLSFQ==") key := lib.StrToBytes("YELLOW SUBMARINE") - ctrFunc := genCTRFunc(0) + ctrFunc := lib.AESGenCTRFunc(0) plain, err := lib.AESDecryptCTR(cipher, key, ctrFunc) if err != nil { fmt.Printf("decryption failed: %v", err) @@ -3,6 +3,29 @@ package lib +// Generates counter function for AES CTR mode. +func AESGenCTRFunc(nonce uint64) func() []byte { + ctr := uint64(0) // Counter + ff := uint64(0xFF) + cf := func() []byte { + cb := make([]byte, 16) // counter block + var i, j uint + // Put nonce in the first 8 bytes in cb in little endian format + for i = 0; i < 8; i++ { + n := nonce & (ff << (i * 8)) // Reset all except the i^th byte of the nonce + cb[i] = byte(n >> (i * 8)) // Retrieve i^th byte of the nonce + } + // Put counter in the next 8 bytes in cb in little endian format + for i, j = 8, 0; i < 16; i, j = i+1, j+1 { + n := ctr & (ff << (j * 8)) // Reset all except the j^th byte of the counter + cb[i] = byte(n >> (j * 8)) // Retrieve j^th byte of the counter + } + ctr += 1 // Increment counter by 1 + return cb + } + return cf +} + func AESEncryptCTR(plain, key []byte, ctrFunc func() []byte) ([]byte, error) { if len(key) != 16 { return []byte{}, CPError{"key length != 16"} |