// 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"
}
func AppendSecretEncryptEcb(plaintext, key []byte, prefix bool) []byte {
if prefix == true {
if len(prefixBytes) == 0 {
prefixBytes, _ = bytes.Random(r.Intn(99) + 1)
}
plaintext = append(prefixBytes, plaintext...)
}
secret, _ := base64.StdEncoding.DecodeString("Um9sbGluJyBpbiBteSA1LjAKV2l0aCBteSByYWctdG9wIGRvd24gc28gbXkgaGFpciBjYW4gYmxvdwpUaGUgZ2lybGllcyBvbiBzdGFuZGJ5IHdhdmluZyBqdXN0IHRvIHNheSBoaQpEaWQgeW91IHN0b3A/IE5vLCBJIGp1c3QgZHJvdmUgYnkK")
plaintext = append(plaintext, secret...)
ciphertext, _ := EcbEncrypt(plaintext, key)
return ciphertext
}
func RandomAesMode() (cipher.BlockMode, string, error) {
block, err := aes.NewCipher(NewAesKey())
if err != nil {
return nil, "", err
}
mode := r.Intn(2)
if mode == 1 {
iv, _ := bytes.Random(aes.BlockSize)
encrypter := cipher.NewCBCEncrypter(block, iv)
return encrypter, "CBC", nil
}
encrypter := NewECBEncrypter(block)
return encrypter, "ECB", nil
}
/* 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
}
/* ECB cut and paste * Make a profile_for function that takes an email address and returns * a user object encoded cookie-style ([email protected]&uid=10). * Encrypt the encoded profile with AES ECB, and *supply* this to the * "attacker". Find a way to create a valid admin profile. */ func c13() (actual, expected Result) { expected = "email=XXXXXXXXXXXXXX&uid=1&role=admin" key, _ := bytes.Random(aes.BlockSize) // A 14 byte-long email address will put role= at the end of the second block attackEmail := string(stdBytes.Repeat([]byte("X"), 14)) // admin padded w/ 10 bytes will put admin at the beginning of the second block attackEmail2 := string(stdBytes.Repeat([]byte("X"), 10)) + "admin" profile1 := profile.New(attackEmail) profile2 := profile.New(attackEmail2) encrypted1, err := profile.Encrypt([]byte(profile1), key) if err != nil { log.Println(err) } encrypted2, err := profile.Encrypt([]byte(profile2), key) if err != nil { log.Println(err) } // Use first two blocks of encrypted1 and thirdBlock of encrypted2 to // create the attack ciphertext adminProfile := encrypted1[0:32] thirdBlock := encrypted2[16:32] adminProfile = append(adminProfile, thirdBlock...) decrypted, err := profile.Decrypt(adminProfile, key) if err != nil { log.Fatal(err) } // Parse the modified ciphertext and encode the admin profile parsed := profile.Parse(string(decrypted)) encoded := profile.Encode(parsed) return encoded, expected }
/* 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)
}
// NewAesKey generates a random AES key
func NewAesKey() []byte {
key, _ := bytes.Random(aes.BlockSize)
return key
}