Ejemplo n.º 1
0
/* Byte-at-a-time ECB decryption
* Create a modified oracle function that decrypts an unknown string encrypted
* under ECB-mode with a consistent, but unknown key.
* AES-128-ECB(known-string || unknown-string, key)
 */
func c12() (actual, expected Result) {
	expected = "Rollin' in my 5.0\nWith my rag-top down so my hair can blow\nThe girlies on standby waving just to say hi\nDid you stop? No, I just drove by\n\x01"

	if crypto.GlobalAesKey == nil {
		crypto.GlobalAesKey = crypto.NewAesKey()
	}
	key := crypto.GlobalAesKey

	blocksize := crypto.DetectBlocksize(key)
	secretBlocks := len(crypto.AppendSecretEncryptEcb([]byte(""), key, false)) / blocksize

	var secret []byte

	createDict := func(plaintext []byte, block int) map[int][]byte {
		dict := make(map[int][]byte)
		for b := 0; b <= 255; b++ {
			extra := []byte{byte(b)}
			plaintext := append(plaintext, extra[0])
			ciphertext := crypto.AppendSecretEncryptEcb(plaintext, key, false)
			dict[b] = ciphertext[block*blocksize : blocksize*(block+1)]
		}
		return dict
	}

	for n := 0; n < secretBlocks; n++ {
		for i := 0; i < blocksize; i++ {
			short := stdBytes.Repeat([]byte("A"), blocksize-(i+1))
			plaintext := append(short, secret...)
			dict := createDict(plaintext, n)
			secretCiphertext := crypto.AppendSecretEncryptEcb(short, key, false)

			for char, lookup := range dict {
				if string(secretCiphertext[n*blocksize:blocksize*(n+1)]) == string(lookup) {
					char := []byte{byte(char)}
					secret = append(secret, char...)
				}
			}
		}
	}
	return string(secret), expected
}
Ejemplo n.º 2
0
/* Byte-at-a-time ECB decryption
* Same goal as #12, but prepend a random # of random bytes to input.
* AES-128-ECB(random-#-bytes || input, key)
 */
func c14() (actual, expected Result) {
	expected = "Rollin' in my 5.0\nWith my rag-top down so my hair can blow\nThe girlies on standby waving just to say hi\nDid you stop? No, I just drove by\n\x01"

	if len(crypto.GlobalAesKey) == 0 {
		crypto.GlobalAesKey = crypto.NewAesKey()
	}
	key := crypto.GlobalAesKey

	blocksize := crypto.DetectBlocksize(key)

	createDict := func(plaintext []byte, prefixLength, block int) map[int][]byte {
		dict := make(map[int][]byte)
		for b := 0; b <= 255; b++ {
			extra := []byte{byte(b)}
			plaintext := append(plaintext, extra[0])
			ciphertext := crypto.AppendSecretEncryptEcb(plaintext, key, true)
			dict[b] = ciphertext[(block*blocksize)+prefixLength : (blocksize*(block+1))+prefixLength]
		}
		return dict
	}

	findPrefixLength := func(blocksize int, key []byte) int {
		// If we send 2-3 blocks of repeating bytes, we will see a repeating block
		for i := blocksize * 2; i <= blocksize*3; i++ {
			encrypted := crypto.AppendSecretEncryptEcb(stdBytes.Repeat([]byte("A"), i), key, true)
			numBlocks := len(encrypted) / blocksize

			// Loop through blocks to find a repeat
			for j := 0; j < numBlocks-1; j++ {
				firstBlock := encrypted[j*blocksize : (j+1)*blocksize]
				secondBlock := encrypted[(j+1)*blocksize : (j+2)*blocksize]

				// Repeating block indicates we added enough bytes to make an even block
				if string(firstBlock) == string(secondBlock) {
					return (j+2)*blocksize - i
				}
			}
		}
		return 0
	}

	// Knowing the length of the random prefix bytes, pad input to make a full block
	var secretBlocks int
	prefix := findPrefixLength(blocksize, key)
	// TODO: There must be a better way to account for prefix/16 rounding down and
	// giving 1 too few blocks
	if prefix%blocksize <= 5 {
		secretBlocks += 1
	}
	pad := blocksize - (prefix % blocksize) // prefix + pad = full block
	prefix += pad

	// Figure out how many blocks to solve
	totalBlocks := len(crypto.AppendSecretEncryptEcb([]byte(""), key, true)) / blocksize
	secretBlocks += totalBlocks - (prefix / 16)
	var secret []byte

	for n := 0; n < secretBlocks; n++ {
		for i := 0; i < blocksize; i++ {
			// Send A*pad to pad the prefix to a full block, + A*blocksize-1,
			// blocksize-2, ... until that block of the secret is solved
			short := stdBytes.Repeat([]byte("A"), pad+blocksize-(i+1))
			plaintext := append(short, secret...)

			// Create a dictionary of ciphertexts for every character
			dict := createDict(plaintext, prefix, n)
			secretCiphertext := crypto.AppendSecretEncryptEcb(short, key, true)

			for char, lookup := range dict {
				targetBlock := secretCiphertext[prefix+(n*blocksize) : prefix+(blocksize*(n+1))]
				if string(targetBlock) == string(lookup) {
					char := []byte{byte(char)}
					secret = append(secret, char...)
				}
			}
		}
	}
	return string(secret), expected
}