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expandMask

Sample a polynomial with coefficients uniformly distributed in (-gamma1, gamma1] Used for sampling the masking vector y during signing FIPS 204: ExpandMask (Algorithm 28)

ml_dsa.expandMask

fn expandMask(comptime gamma1_bits: u8, seed: *const [64]u8, nonce: u16) Poly

File

lib/std/crypto/ml_dsa.zig:1398

Code

fn expandMask(comptime gamma1_bits: u8, seed: *const [64]u8, nonce: u16) Poly {
    const packed_size = ((gamma1_bits + 1) * N) / 8;
    var buf: [packed_size]u8 = undefined;

    // Construct IV: seed || nonce (little-endian)
    var iv: [66]u8 = undefined;
    @memcpy(iv[0..64], seed);
    iv[64] = @truncate(nonce & 0xFF);
    iv[65] = @truncate(nonce >> 8);

    var h = sha3.Shake256.init(.{});
    h.update(&iv);
    h.squeeze(&buf);

    // Unpack the polynomial
    return polyUnpackLeGamma1(gamma1_bits, &buf);
}