bip39 2.2.2

Library for BIP-39 Bitcoin mnemonic codes
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128

use bitcoin_hashes::{hmac, sha512, Hash, HashEngine};

const SALT_PREFIX: &'static str = "mnemonic";

/// Calculate the binary size of the mnemonic.
fn mnemonic_byte_len<M>(mnemonic: M) -> usize
	where M: Iterator<Item = &'static str> + Clone,
{
	let mut len = 0;
	for (i, word) in mnemonic.enumerate() {
		if i > 0 {
			len += 1;
		}
		len += word.len();
	}
	len
}

/// Wrote the mnemonic in binary form into the hash engine.
fn mnemonic_write_into<M>(mnemonic: M, engine: &mut sha512::HashEngine)
	where M: Iterator<Item = &'static str> + Clone,
{
	for (i, word) in mnemonic.enumerate() {
		if i > 0 {
			engine.input(" ".as_bytes());
		}
		engine.input(word.as_bytes());
	}
}

/// Create an HMAC engine from the passphrase.
/// We need a special method because we can't allocate a new byte
/// vector for the entire serialized mnemonic.
fn create_hmac_engine<M>(mnemonic: M) -> hmac::HmacEngine<sha512::Hash>
	where M: Iterator<Item = &'static str> + Clone,
{
	// Inner code is borrowed from the bitcoin_hashes::hmac::HmacEngine::new method.
	let mut ipad = [0x36u8; 128];
	let mut opad = [0x5cu8; 128];
	let mut iengine = sha512::Hash::engine();
	let mut oengine = sha512::Hash::engine();

	if mnemonic_byte_len(mnemonic.clone()) > sha512::HashEngine::BLOCK_SIZE {
		let hash = {
			let mut engine = sha512::Hash::engine();
			mnemonic_write_into(mnemonic, &mut engine);
			sha512::Hash::from_engine(engine)
		};

		for (b_i, b_h) in ipad.iter_mut().zip(&hash[..]) {
			*b_i ^= *b_h;
		}
		for (b_o, b_h) in opad.iter_mut().zip(&hash[..]) {
			*b_o ^= *b_h;
		}
	} else {
		// First modify the first elements from the prefix.
		let mut cursor = 0;
		for (i, word) in mnemonic.enumerate() {
			if i > 0 {
				ipad[cursor] ^= ' ' as u8;
				opad[cursor] ^= ' ' as u8;
				cursor += 1;
			}
			for (b_i, b_h) in ipad.iter_mut().skip(cursor).zip(word.as_bytes()) {
				*b_i ^= *b_h;
			}
			for (b_o, b_h) in opad.iter_mut().skip(cursor).zip(word.as_bytes()) {
				*b_o ^= *b_h;
			}
			cursor += word.len();
			assert!(cursor <= sha512::HashEngine::BLOCK_SIZE, "mnemonic_byte_len is broken");
		}
	};

	iengine.input(&ipad[..sha512::HashEngine::BLOCK_SIZE]);
	oengine.input(&opad[..sha512::HashEngine::BLOCK_SIZE]);
	hmac::HmacEngine::from_inner_engines(iengine, oengine)
}

// Method borrowed from rust-bitcoin's endian module.
#[inline]
fn u32_to_array_be(val: u32) -> [u8; 4] {
	let mut res = [0; 4];
	for i in 0..4 {
		res[i] = ((val >> (4 - i - 1) * 8) & 0xff) as u8;
	}
	res
}

#[inline]
fn xor(res: &mut [u8], salt: &[u8]) {
	debug_assert!(salt.len() >= res.len(), "length mismatch in xor");

	res.iter_mut().zip(salt.iter()).for_each(|(a, b)| *a ^= b);
}

/// PBKDF2-HMAC-SHA512 implementation using bitcoin_hashes.
pub(crate) fn pbkdf2<M>(mnemonic: M, unprefixed_salt: &[u8], c: usize, res: &mut [u8])
	where M: Iterator<Item = &'static str> + Clone,
{
	let prf = create_hmac_engine(mnemonic);

	for (i, chunk) in res.chunks_mut(sha512::Hash::LEN).enumerate() {
		for v in chunk.iter_mut() {
			*v = 0;
		}

		let mut salt = {
			let mut prfc = prf.clone();
			prfc.input(SALT_PREFIX.as_bytes());
			prfc.input(unprefixed_salt);
			prfc.input(&u32_to_array_be((i + 1) as u32));

			let salt = hmac::Hmac::from_engine(prfc).to_byte_array();
			xor(chunk, &salt);
			salt
		};

		for _ in 1..c {
			let mut prfc = prf.clone();
			prfc.input(&salt);
			salt = hmac::Hmac::from_engine(prfc).to_byte_array();

			xor(chunk, &salt);
		}
	}
}