// AesOracle prepends and appends 5-10 random bytes to a plaintext,
// encrypts the plaintext under a predetermined BlockMode, then
// returns the detected BlockMode
func AesOracle(plaintext []byte, encrypter cipher.BlockMode) string {
// Generate random bytes to prepend/append to plaintext
prependBytes, _ := bytes.Random(r.Intn(5) + 5)
appendBytes, _ := bytes.Random(r.Intn(5) + 5)
plaintext = append(prependBytes, plaintext...)
plaintext = append(plaintext, appendBytes...)
plaintext, _ = blocks.Pkcs7(plaintext, aes.BlockSize)
ciphertext := make([]byte, len(plaintext))
modifiedCiphertext := make([]byte, len(plaintext))
// Modify the first block of the plaintext
modified := plaintext
modified[0] = byte(255)
encrypter.CryptBlocks(ciphertext, plaintext)
encrypter.CryptBlocks(modifiedCiphertext, modified)
// If the second block in the modified ciphertext is affected by a
// change in the first block of the plaintext, return CBC mode
if ciphertext[16] != modifiedCiphertext[16] {
return "CBC"
}
return "ECB"
}
// Implement PKCS#/ padding
func c9() (actual, expected Result) {
input := "YELLOW SUBMARINE"
expected = "YELLOW SUBMARINE\x04\x04\x04\x04"
padded, err := blocks.Pkcs7([]byte(input), 20)
if err != nil {
log.Fatal(err)
}
return string(padded), expected
}
func EcbEncrypt(plaintext, key []byte) ([]byte, error) {
plaintext, _ = blocks.Pkcs7(plaintext, aes.BlockSize)
block, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
ciphertext := make([]byte, len(plaintext))
encrypter := NewECBEncrypter(block)
encrypter.CryptBlocks(ciphertext, plaintext)
return ciphertext, nil
}