ferogram_crypto/
rsa.rs

1// Copyright (c) Ankit Chaubey <ankitchaubey.dev@gmail.com>
2// SPDX-License-Identifier: MIT OR Apache-2.0
3//
4// ferogram: async Telegram MTProto client in Rust
5// https://github.com/ankit-chaubey/ferogram
6//
7// If you use or modify this code, keep this notice at the top of your file
8// and include the LICENSE-MIT or LICENSE-APACHE file from this repository:
9// https://github.com/ankit-chaubey/ferogram
10
11use crate::{aes, sha256};
12use num_bigint::BigUint;
13
14/// An RSA public key (n, e).
15pub struct Key {
16    n: BigUint,
17    e: BigUint,
18}
19
20impl Key {
21    /// Parse decimal `n` and `e` strings.
22    pub fn new(n: &str, e: &str) -> Option<Self> {
23        Some(Self {
24            n: BigUint::parse_bytes(n.as_bytes(), 10)?,
25            e: BigUint::parse_bytes(e.as_bytes(), 10)?,
26        })
27    }
28}
29
30fn increment(data: &mut [u8]) {
31    let mut i = data.len() - 1;
32    loop {
33        let (n, overflow) = data[i].overflowing_add(1);
34        data[i] = n;
35        if overflow {
36            i = i.checked_sub(1).unwrap_or(data.len() - 1);
37        } else {
38            break;
39        }
40    }
41}
42
43/// RSA-encrypt `data` using the MTProto RSA-PAD scheme.
44///
45/// `random_bytes` must be exactly 224 bytes of secure random data.
46/// `data` must be ≤ 144 bytes.
47pub fn encrypt_hashed(data: &[u8], key: &Key, random_bytes: &[u8; 224]) -> Vec<u8> {
48    assert!(data.len() <= 144, "data too large for RSA-PAD");
49
50    // data_with_padding: 192 bytes
51    let mut data_with_padding = Vec::with_capacity(192);
52    data_with_padding.extend_from_slice(data);
53    data_with_padding.extend_from_slice(&random_bytes[..192 - data.len()]);
54
55    // data_pad_reversed
56    let data_pad_reversed: Vec<u8> = data_with_padding.iter().copied().rev().collect();
57
58    let mut temp_key: [u8; 32] = random_bytes[192..].try_into().unwrap();
59
60    let key_aes_encrypted = loop {
61        // data_with_hash = data_pad_reversed + SHA256(temp_key + data_with_padding)
62        let mut data_with_hash = Vec::with_capacity(224);
63        data_with_hash.extend_from_slice(&data_pad_reversed);
64        data_with_hash.extend_from_slice(&sha256!(&temp_key, &data_with_padding));
65
66        aes::ige_encrypt(&mut data_with_hash, &temp_key, &[0u8; 32]);
67
68        // temp_key_xor = temp_key XOR SHA256(aes_encrypted)
69        let hash = sha256!(&data_with_hash);
70        let mut xored = temp_key;
71        for (a, b) in xored.iter_mut().zip(hash.iter()) {
72            *a ^= b;
73        }
74
75        let mut candidate = Vec::with_capacity(256);
76        candidate.extend_from_slice(&xored);
77        candidate.extend_from_slice(&data_with_hash);
78
79        if BigUint::from_bytes_be(&candidate) < key.n {
80            break candidate;
81        }
82        increment(&mut temp_key);
83    };
84
85    let payload = BigUint::from_bytes_be(&key_aes_encrypted);
86    let encrypted = payload.modpow(&key.e, &key.n);
87    let mut block = encrypted.to_bytes_be();
88    while block.len() < 256 {
89        block.insert(0, 0);
90    }
91    block
92}
ferogram_crypto/rsa.rs

ferogram_crypto/
rsa.rs
