NistDRBG

const NistDRBG = struct

File

Code

const NistDRBG = struct {
    key: [32]u8,
    v: [16]u8,

    fn incV(g: *NistDRBG) void {
        const val = std.mem.readInt(u128, &g.v, .big);
        std.mem.writeInt(u128, &g.v, val +% 1, .big);
    }

    // AES256_CTR_DRBG_Update(pd, &g.key, &g.v).
    fn update(g: *NistDRBG, pd: ?[48]u8) void {
        var buf: [48]u8 = undefined;
        const ctx = crypto.core.aes.Aes256.initEnc(g.key);
        var i: usize = 0;
        while (i < 3) : (i += 1) {
            g.incV();
            var block: [16]u8 = undefined;
            ctx.encrypt(&block, &g.v);
            buf[i * 16 ..][0..16].* = block;
        }
        if (pd) |p| {
            for (&buf, p) |*b, x| {
                b.* ^= x;
            }
        }
        g.key = buf[0..32].*;
        g.v = buf[32..48].*;
    }

    // randombytes.
    fn fill(g: *NistDRBG, out: []u8) void {
        var block: [16]u8 = undefined;
        var dst = out;

        const ctx = crypto.core.aes.Aes256.initEnc(g.key);
        while (dst.len > 0) {
            g.incV();
            ctx.encrypt(&block, &g.v);
            if (dst.len < 16) {
                @memcpy(dst, block[0..dst.len]);
                break;
            }
            dst[0..block.len].* = block;
            dst = dst[16..dst.len];
        }
        g.update(null);
    }

    fn init(seed: [48]u8) NistDRBG {
        var ret: NistDRBG = .{ .key = @splat(0), .v = @splat(0) };
        ret.update(seed);
        return ret;
    }
}