webrtc_dtls/crypto/
crypto_gcm.rs

1// AES-GCM (Galois Counter Mode)
2// The most widely used block cipher worldwide.
3// Mandatory as of TLS 1.2 (2008) and used by default by most clients.
4// RFC 5288 year 2008 https://tools.ietf.org/html/rfc5288
5
6// https://github.com/RustCrypto/AEADs
7// https://docs.rs/aes-gcm/0.8.0/aes_gcm/
8
9use std::io::Cursor;
10
11use aes_gcm::aead::generic_array::GenericArray;
12use aes_gcm::aead::AeadInPlace;
13use aes_gcm::{Aes128Gcm, KeyInit};
14use rand::Rng;
15
16use super::*;
17use crate::content::*;
18use crate::error::*;
19use crate::record_layer::record_layer_header::*; // what about Aes256Gcm?
20
21const CRYPTO_GCM_TAG_LENGTH: usize = 16;
22const CRYPTO_GCM_NONCE_LENGTH: usize = 12;
23
24// State needed to handle encrypted input/output
25#[derive(Clone)]
26pub struct CryptoGcm {
27    local_gcm: Aes128Gcm,
28    remote_gcm: Aes128Gcm,
29    local_write_iv: Vec<u8>,
30    remote_write_iv: Vec<u8>,
31}
32
33impl CryptoGcm {
34    pub fn new(
35        local_key: &[u8],
36        local_write_iv: &[u8],
37        remote_key: &[u8],
38        remote_write_iv: &[u8],
39    ) -> Self {
40        let key = GenericArray::from_slice(local_key);
41        let local_gcm = Aes128Gcm::new(key);
42
43        let key = GenericArray::from_slice(remote_key);
44        let remote_gcm = Aes128Gcm::new(key);
45
46        CryptoGcm {
47            local_gcm,
48            local_write_iv: local_write_iv.to_vec(),
49            remote_gcm,
50            remote_write_iv: remote_write_iv.to_vec(),
51        }
52    }
53
54    pub fn encrypt(&self, pkt_rlh: &RecordLayerHeader, raw: &[u8]) -> Result<Vec<u8>> {
55        let payload = &raw[RECORD_LAYER_HEADER_SIZE..];
56        let raw = &raw[..RECORD_LAYER_HEADER_SIZE];
57
58        let mut nonce = vec![0u8; CRYPTO_GCM_NONCE_LENGTH];
59        nonce[..4].copy_from_slice(&self.local_write_iv[..4]);
60        rand::thread_rng().fill(&mut nonce[4..]);
61        let nonce = GenericArray::from_slice(&nonce);
62
63        let additional_data = generate_aead_additional_data(pkt_rlh, payload.len());
64
65        let mut buffer: Vec<u8> = Vec::new();
66        buffer.extend_from_slice(payload);
67
68        self.local_gcm
69            .encrypt_in_place(nonce, &additional_data, &mut buffer)
70            .map_err(|e| Error::Other(e.to_string()))?;
71
72        let mut r = Vec::with_capacity(raw.len() + nonce.len() + buffer.len());
73        r.extend_from_slice(raw);
74        r.extend_from_slice(&nonce[4..]);
75        r.extend_from_slice(&buffer);
76
77        // Update recordLayer size to include explicit nonce
78        let r_len = (r.len() - RECORD_LAYER_HEADER_SIZE) as u16;
79        r[RECORD_LAYER_HEADER_SIZE - 2..RECORD_LAYER_HEADER_SIZE]
80            .copy_from_slice(&r_len.to_be_bytes());
81
82        Ok(r)
83    }
84
85    pub fn decrypt(&self, r: &[u8]) -> Result<Vec<u8>> {
86        let mut reader = Cursor::new(r);
87        let h = RecordLayerHeader::unmarshal(&mut reader)?;
88        if h.content_type == ContentType::ChangeCipherSpec {
89            // Nothing to encrypt with ChangeCipherSpec
90            return Ok(r.to_vec());
91        }
92
93        if r.len() <= (RECORD_LAYER_HEADER_SIZE + 8) {
94            return Err(Error::ErrNotEnoughRoomForNonce);
95        }
96
97        let mut nonce = vec![];
98        nonce.extend_from_slice(&self.remote_write_iv[..4]);
99        nonce.extend_from_slice(&r[RECORD_LAYER_HEADER_SIZE..RECORD_LAYER_HEADER_SIZE + 8]);
100        let nonce = GenericArray::from_slice(&nonce);
101
102        let out = &r[RECORD_LAYER_HEADER_SIZE + 8..];
103
104        let additional_data = generate_aead_additional_data(&h, out.len() - CRYPTO_GCM_TAG_LENGTH);
105
106        let mut buffer: Vec<u8> = Vec::new();
107        buffer.extend_from_slice(out);
108
109        self.remote_gcm
110            .decrypt_in_place(nonce, &additional_data, &mut buffer)
111            .map_err(|e| Error::Other(e.to_string()))?;
112
113        let mut d = Vec::with_capacity(RECORD_LAYER_HEADER_SIZE + buffer.len());
114        d.extend_from_slice(&r[..RECORD_LAYER_HEADER_SIZE]);
115        d.extend_from_slice(&buffer);
116
117        Ok(d)
118    }
119}
webrtc_dtls/crypto/crypto_gcm.rs

webrtc_dtls/crypto/
crypto_gcm.rs
