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// Copyright © 2020 rsiddharth <s@ricketyspace.net>
// SPDX-License-Identifier: ISC
package lib
import (
"crypto/rand"
"math/big"
)
// 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
}
// Randomly generates `min` to `max` bytes.
func randomBytes(min, max int64) []byte {
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 {
break
}
}
bs := make([]byte, rn.Int64())
_, err = rand.Read(bs)
if err != nil {
panic(err)
}
return bs
}
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