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HKDF allow expansion up to, and including <hash size> * 255 bytes (#14051)

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Fixes #14050
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Frank Denis 2022-12-23 22:38:27 +01:00 committed by GitHub
parent 581d292381
commit c9e3524d0b
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1 changed files with 3 additions and 2 deletions
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5
lib/std/crypto/hkdf.zig
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@ -22,7 +22,7 @@ pub fn Hkdf(comptime Hmac: type) type {
/// Derive a subkey from a master key `prk` and a subkey description `ctx`.
pub fn expand(out: []u8, ctx: []const u8, prk: [Hmac.mac_length]u8) void {
assert(out.len < Hmac.mac_length * 255); // output size is too large for the Hkdf construction
assert(out.len <= Hmac.mac_length * 255); // output size is too large for the Hkdf construction
var i: usize = 0;
var counter = [1]u8{1};
while (i + Hmac.mac_length <= out.len) : (i += Hmac.mac_length) {
@ -33,7 +33,8 @@ pub fn Hkdf(comptime Hmac: type) type {
st.update(ctx);
st.update(&counter);
st.final(out[i..][0..Hmac.mac_length]);
counter[0] += 1;
counter[0] +%= 1;
assert(counter[0] != 1);
}
const left = out.len % Hmac.mac_length;
if (left > 0) {