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use ring::digest;
use ring::hmac;
use std::io::Write;
fn convert_digest_to_hmac_alg(hash: &'static digest::Algorithm) -> hmac::Algorithm {
if hash == &digest::SHA256 {
hmac::HMAC_SHA256
} else if hash == &digest::SHA384 {
hmac::HMAC_SHA384
} else if hash == &digest::SHA512 {
hmac::HMAC_SHA512
} else {
panic!("bad digest for prf");
}
}
fn concat_sign(key: &hmac::Key, a: &[u8], b: &[u8]) -> hmac::Tag {
let mut ctx = hmac::Context::with_key(key);
ctx.update(a);
ctx.update(b);
ctx.sign()
}
fn p(out: &mut [u8], hashalg: &'static digest::Algorithm, secret: &[u8], seed: &[u8]) {
let hmac_key = hmac::Key::new(convert_digest_to_hmac_alg(hashalg), secret);
let mut current_a = hmac::sign(&hmac_key, seed);
let mut offs = 0;
while offs < out.len() {
let p_term = concat_sign(&hmac_key, current_a.as_ref(), seed);
offs += out[offs..].as_mut().write(p_term.as_ref()).unwrap();
current_a = hmac::sign(&hmac_key, current_a.as_ref());
}
}
fn concat(a: &[u8], b: &[u8]) -> Vec<u8> {
let mut ret = Vec::new();
ret.extend_from_slice(a);
ret.extend_from_slice(b);
ret
}
pub fn prf(out: &mut [u8],
hashalg: &'static digest::Algorithm,
secret: &[u8],
label: &[u8],
seed: &[u8]) {
let joined_seed = concat(label, seed);
p(out, hashalg, secret, &joined_seed);
}
#[cfg(test)]
mod tests {
use ring::digest::{SHA256, SHA512};
#[test]
fn check_sha256() {
let secret = b"\x9b\xbe\x43\x6b\xa9\x40\xf0\x17\xb1\x76\x52\x84\x9a\x71\xdb\x35";
let seed = b"\xa0\xba\x9f\x93\x6c\xda\x31\x18\x27\xa6\xf7\x96\xff\xd5\x19\x8c";
let label = b"test label";
let expect = include_bytes!("testdata/prf-result.1.bin");
let mut output = [0u8; 100];
super::prf(&mut output, &SHA256, secret, label, seed);
assert_eq!(expect.len(), output.len());
assert_eq!(expect.to_vec(), output.to_vec());
}
#[test]
fn check_sha512() {
let secret = b"\xb0\x32\x35\x23\xc1\x85\x35\x99\x58\x4d\x88\x56\x8b\xbb\x05\xeb";
let seed = b"\xd4\x64\x0e\x12\xe4\xbc\xdb\xfb\x43\x7f\x03\xe6\xae\x41\x8e\xe5";
let label = b"test label";
let expect = include_bytes!("testdata/prf-result.2.bin");
let mut output = [0u8; 196];
super::prf(&mut output, &SHA512, secret, label, seed);
assert_eq!(expect.len(), output.len());
assert_eq!(expect.to_vec(), output.to_vec());
}
}