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-rw-r--r--challenge/c18.go24
-rw-r--r--lib/aes.go23
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)
diff --git a/lib/aes.go b/lib/aes.go
index 82ee8ed..f3fd6d9 100644
--- a/lib/aes.go
+++ b/lib/aes.go
@@ -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"}