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// Copyright © 2020 rsiddharth <s@ricketyspace.net>
// SPDX-License-Identifier: ISC
package lib
import (
"crypto/rand"
"math/big"
)
var oracleUnknown string = `Um9sbGluJyBpbiBteSA1LjAKV2l0aCBteSByYWctdG9wIGRvd24gc28gbXkg
aGFpciBjYW4gYmxvdwpUaGUgZ2lybGllcyBvbiBzdGFuZGJ5IHdhdmluZyBq
dXN0IHRvIHNheSBoaQpEaWQgeW91IHN0b3A/IE5vLCBJIGp1c3QgZHJvdmUg
YnkK`
var oracleKey []byte = make([]byte, 16)
var oracleRandom []byte = make([]byte, randomInt(1, 16))
func init() {
_, err := rand.Read(oracleKey)
if err != nil {
panic(err)
}
_, err = rand.Read(oracleRandom)
if err != nil {
panic(err)
}
}
// Given an input `in`, this function AES encrypts `in` using a
// randomly generate 16-byte key using ECB or CBC mode and returns the
// cipher.
func OracleAESRandomEncrypt(in []byte) []byte {
// Generate random key.
key := make([]byte, 16)
_, err := rand.Read(key)
if err != nil {
panic(err)
}
// Generate random initialization vector; needed for AES CBC.
iv := make([]byte, 16)
_, err = rand.Read(iv)
if err != nil {
panic(err)
}
// Add 5-10 bytes at the beginning and end of `in`
in = append(randomBytes(5, 10), in...)
in = append(in, randomBytes(5, 10)...)
// Randomly encrypt `in` with AES in ECB or CBC mode.
m, err := rand.Int(rand.Reader, big.NewInt(2))
if err != nil {
panic(err)
}
var out []byte
if m.Int64() == 0 {
// Encrypt with AES in ECB mode.
out = AESEncryptECB(in, key)
} else {
// Encrypt with AES in CBC mode.
out = AESEncryptCBC(in, key, iv)
}
return out
}
func OracleAESEncryptECB(in []byte) []byte {
return AESEncryptECB(append(in, Base64ToBytes(oracleUnknown)...), oracleKey)
}
// Return a random number from range [min, max]
func randomInt(min, max int64) int64 {
if min >= max {
panic("randomInt: min cannot be >= max!")
}
var rn *big.Int
var err error
for {
rn, err = rand.Int(rand.Reader, big.NewInt(max+1))
if err != nil {
panic(err)
}
if rn.Int64() >= min {
return rn.Int64()
}
}
}
// Randomly generates `min` to `max` bytes.
func randomBytes(min, max int64) []byte {
bs := make([]byte, randomInt(min, max))
_, err := rand.Read(bs)
if err != nil {
panic(err)
}
return bs
}
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