예제 #1
0
/* CBC bitflipping attack
* Create a function, that given an input, prepends:
* "comment1=cooking%20MCs;userdata="
* and appends:
* ";comment2=%20like%20a%20pound%20of%20bacon"
* , quotes out the ; and =, and pads and encrypts it under AES CBC.
* Another function should decrypt the string and return true if
* ";admin=true;" exists in the string. Modify the ciphertext to
* make the second funcion return true.
 */
func c16() (actual, expected Result) {
	key := crypto.NewAesKey()

	input := "XadminXtrue"
	inputBytes := []byte(input)
	str := profile.ProcessComment(input)

	iv, _ := bytes.Random(aes.BlockSize)
	encrypted, err := crypto.CbcEncrypt([]byte(str), key, iv)
	if err != nil {
		panic(err)
	}

	// Flip the targeted bytes ("X"s in the input string)
	encrypted[16] = encrypted[16] ^ 59 ^ inputBytes[0]
	encrypted[22] = encrypted[22] ^ 61 ^ inputBytes[6]

	hasAdmin := profile.HasAdmin(encrypted, key, iv)
	return hasAdmin, true
}
예제 #2
0
/* CBC padding oracle
* Write a CBC padding oracle that decrypts a ciphertext and detects
* if the plaintext is padded properly with PKCS#7. Choose a random line
* from 17.txt, encrypt it, then decrypt it using the oracle.
 */
func c17() (actual, expected Result) {
	input, _ := ioutil.ReadFile("input/17.txt")
	strs := strings.Split(string(input), "\n")
	str := strs[r.Intn(10)]
	decodedStr, _ := base64.StdEncoding.DecodeString(str)

	if crypto.GlobalAesKey == nil {
		crypto.GlobalAesKey = crypto.NewAesKey()
	}
	key := crypto.GlobalAesKey
	iv, _ := bytes.Random(aes.BlockSize)

	ciphertext, err := crypto.CbcEncrypt([]byte(decodedStr), key, iv)
	if err != nil {
		log.Fatal(err)
	}

	blocks, err := bytes.SplitIntoBlocks(ciphertext, aes.BlockSize)
	if err != nil {
		log.Fatal(err)
	}

	var plaintext []byte

	for n := 0; n < len(blocks); n++ {
		block := blocks[n]
		controlled := make([]byte, aes.BlockSize)
		plaintextBlock := make([]byte, aes.BlockSize)
		intermediate := make([]byte, aes.BlockSize)
		prevBlock := make([]byte, aes.BlockSize)

		if n == 0 {
			prevBlock = iv
		} else {
			prevBlock = blocks[n-1]
		}

		for i := aes.BlockSize - 1; i >= 0; i-- {
			paddingLen := aes.BlockSize - i
			paddingByte := byte(paddingLen)

			// Set the last paddingLen bytes of controlled to so that when decrypted,
			// each will be a valid padding byte.
			for j := 0; j < paddingLen; j++ {
				controlled[i+j] = paddingByte ^ intermediate[i+j]
			}

			for b := 0; b <= 256; b++ {
				controlled[i] = byte(b)
				controlled := append(controlled, block...)
				valid, _ := crypto.CbcPaddingOracle(controlled, iv)
				if valid {
					// The padding is valid and we control the ith byte of the
					// block XORed with the intermediate state. XOR is an inverse
					// operation so finding the ith byte of the intermediate state
					// is as simple as:
					intermediate[i] = paddingByte ^ controlled[i]
					break
				}
			}
			plaintextBlock[i] = prevBlock[i] ^ intermediate[i]
		}
		plaintext = append(plaintext, plaintextBlock...)
	}

	decrypted, _ := crypto.CbcDecrypt(ciphertext, key, iv)
	return string(plaintext), string(decrypted)
}