Source
pub fn hmacExpandLabel(
comptime Hmac: type,
secret: []const u8,
label_then_seed: []const []const u8,
comptime len: usize,
) [len]u8 {
const initial_hmac: Hmac = .init(secret);
var a: [Hmac.mac_length]u8 = undefined;
var result: [std.mem.alignForwardAnyAlign(usize, len, Hmac.mac_length)]u8 = undefined;
var index: usize = 0;
while (index < result.len) : (index += Hmac.mac_length) {
var a_hmac = initial_hmac;
if (index > 0) a_hmac.update(&a) else for (label_then_seed) |part| a_hmac.update(part);
a_hmac.final(&a);
var result_hmac = initial_hmac;
result_hmac.update(&a);
for (label_then_seed) |part| result_hmac.update(part);
result_hmac.final(result[index..][0..Hmac.mac_length]);
}
return result[0..len].*;
}