527 lines
20 KiB
Zig
527 lines
20 KiB
Zig
const std = @import("std");
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const assert = std.debug.assert;
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const crypto = std.crypto;
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const debug = std.debug;
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const mem = std.mem;
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const math = std.math;
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const modes = crypto.core.modes;
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const Cmac = @import("cmac.zig").Cmac;
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const AuthenticationError = crypto.errors.AuthenticationError;
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pub const Aes128Siv = AesSiv(crypto.core.aes.Aes128);
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pub const Aes256Siv = AesSiv(crypto.core.aes.Aes256);
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/// AES-SIV: Deterministic authenticated encryption - the same message always produces the same ciphertext.
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///
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/// What it does: Encrypts data and protects it from tampering. Unlike most encryption modes,
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/// AES-SIV is deterministic: encrypting the same message with the same key always produces
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/// the same ciphertext (unless you provide an optional nonce).
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///
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/// When to use AES-SIV:
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/// - When you need deterministic encryption (e.g., for deduplication in encrypted storage)
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/// - When you can't store or generate nonces
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/// - For key wrapping (protecting cryptographic keys)
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/// - When you need to search encrypted data without decrypting it
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///
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/// When NOT to use AES-SIV:
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/// - When identical plaintexts must produce different ciphertexts (use AES-GCM or AES-GCM-SIV)
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/// - For network protocols where replay attacks are a concern
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///
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/// Unique features:
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/// - Optional nonce: You can add a nonce to make encryption non-deterministic, but this is optional
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/// - Multiple associated data: Supports a vector of associated data strings instead of just one.
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/// The algorithm cryptographically ensures each component is properly separated, preventing
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/// canonicalization attacks where different splits of data could be accepted as valid.
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///
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/// Security properties:
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/// - Deterministic: Same input always gives same output (this can leak information about patterns)
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/// - Nonce misuse resistant: Doesn't catastrophically fail if you reuse a nonce
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/// - Key commitment: Ciphertext can only be decrypted with the exact key that encrypted it
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///
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/// AES-SIV has better security properties than AES-GCM-SIV, but is must slower.
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///
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/// How it works: Combines two keys - one for authentication (S2V) and one for encryption (CTR mode).
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/// The total key size is double the AES key size (256 bits for AES-128-SIV, 512 bits for AES-256-SIV).
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///
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/// Defined in RFC 5297.
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fn AesSiv(comptime Aes: anytype) type {
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debug.assert(Aes.block.block_length == 16);
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return struct {
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pub const tag_length = 16;
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pub const key_length = Aes.key_bits / 8 * 2; // SIV uses 2x key size
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const CmacImpl = Cmac(Aes);
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/// S2V (String to Vector) - RFC 5297 Section 2.4
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/// Derives a synthetic IV from the key and input strings using CMAC.
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/// This function implements a cryptographic pseudo-random function that maps
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/// a variable-length vector of strings to a fixed 128-bit output.
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fn s2v(iv: *[16]u8, key: [Aes.key_bits / 8]u8, strings: []const []const u8) void {
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assert(strings.len > 0);
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assert(strings.len <= 127); // S2V limitation
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var d: [16]u8 = undefined;
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// Special case: single empty string
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if (strings.len == 1 and strings[0].len == 0) {
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CmacImpl.create(&d, &[_]u8{}, &key);
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iv.* = d;
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return;
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}
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// Initialize with CMAC of zero block
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const zero_block: [16]u8 = @splat(0);
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CmacImpl.create(&d, &zero_block, &key);
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// Process all strings except the last one
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var i: usize = 0;
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while (i < strings.len - 1) : (i += 1) {
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d = dbl(d);
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var tmp: [16]u8 = undefined;
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CmacImpl.create(&tmp, strings[i], &key);
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for (&d, tmp) |*b, t| {
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b.* ^= t;
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}
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}
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// Process the final string
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const sn = strings[strings.len - 1];
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if (sn.len >= 16) {
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// XOR d with the last 16 bytes of Sn,
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// and give the entire Sn to CMAC incrementally.
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var cmac = CmacImpl.init(&key);
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const prefix = sn.len - 16;
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cmac.update(sn[0..prefix]);
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var tail: [16]u8 = undefined;
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for (&tail, sn[prefix..][0..16], d) |*out, s, db| {
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out.* = s ^ db;
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}
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cmac.update(&tail);
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cmac.final(iv);
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} else {
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// Pad and XOR
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d = dbl(d);
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var padded: [16]u8 = @splat(0);
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@memcpy(padded[0..sn.len], sn);
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padded[sn.len] = 0x80;
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for (&d, padded) |*b, p| {
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b.* ^= p;
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}
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CmacImpl.create(iv, &d, &key);
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}
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}
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/// Double operation as defined in RFC 5297.
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/// Performs multiplication by x (i.e., left shift by 1) in GF(2^128).
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/// This is the same operation used in CMAC subkey generation.
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/// If the MSB is set, XORs with the polynomial 0x87 after shifting.
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fn dbl(d: [16]u8) [16]u8 {
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// Read as big-endian 128-bit integer
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const val = mem.readInt(u128, &d, .big);
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// Left shift by 1, and XOR with 0x87 if MSB was set
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const doubled = (val << 1) ^ (0x87 & -%(@as(u128, val >> 127)));
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// Write back as big-endian
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var result: [16]u8 = undefined;
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mem.writeInt(u128, &result, doubled, .big);
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return result;
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}
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/// Encrypt plaintext using AES-SIV
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/// `c`: Output buffer for ciphertext (same size as plaintext)
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/// `tag`: Output buffer for authentication tag (synthetic IV)
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/// `m`: Plaintext to encrypt
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/// `ad`: Optional associated data
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/// `nonce`: Optional nonce (if provided, will be added as last AD component)
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/// `key`: Combined key (2x AES key size)
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pub fn encrypt(c: []u8, tag: *[tag_length]u8, m: []const u8, ad: ?[]const u8, nonce: ?[]const u8, key: [key_length]u8) void {
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debug.assert(c.len == m.len);
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// Split key into K1 (for S2V) and K2 (for CTR)
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const k1 = key[0 .. Aes.key_bits / 8];
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const k2 = key[Aes.key_bits / 8 ..];
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// Prepare strings for S2V: AD components followed by plaintext
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var strings_buf: [128][]const u8 = undefined;
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var strings_len: usize = 0;
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if (ad) |a| {
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strings_buf[strings_len] = a;
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strings_len += 1;
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}
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if (nonce) |n| {
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strings_buf[strings_len] = n;
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strings_len += 1;
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}
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strings_buf[strings_len] = m;
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strings_len += 1;
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// Compute synthetic IV using S2V
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s2v(tag, k1.*, strings_buf[0..strings_len]);
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// Clear the 31st and 63rd bits for use as CTR IV
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var ctr_iv = tag.*;
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ctr_iv[8] &= 0x7f;
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ctr_iv[12] &= 0x7f;
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// Encrypt plaintext using CTR mode
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const aes_ctx = Aes.initEnc(k2.*);
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modes.ctr(@TypeOf(aes_ctx), aes_ctx, c, m, ctr_iv, .big);
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}
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/// Decrypt ciphertext using AES-SIV
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/// `m`: Output buffer for decrypted plaintext
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/// `c`: Ciphertext to decrypt
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/// `tag`: Authentication tag (synthetic IV)
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/// `ad`: Optional associated data (must match encryption)
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/// `nonce`: Optional nonce (must match encryption)
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/// `key`: Combined key (2x AES key size)
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pub fn decrypt(m: []u8, c: []const u8, tag: [tag_length]u8, ad: ?[]const u8, nonce: ?[]const u8, key: [key_length]u8) AuthenticationError!void {
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assert(c.len == m.len);
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// Split key into K1 (for S2V) and K2 (for CTR)
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const k1 = key[0 .. Aes.key_bits / 8];
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const k2 = key[Aes.key_bits / 8 ..];
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// Clear the 31st and 63rd bits for use as CTR IV
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var ctr_iv = tag;
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ctr_iv[8] &= 0x7f;
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ctr_iv[12] &= 0x7f;
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// Decrypt ciphertext using CTR mode
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const aes_ctx = Aes.initEnc(k2.*);
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modes.ctr(@TypeOf(aes_ctx), aes_ctx, m, c, ctr_iv, .big);
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// Prepare strings for S2V: AD components followed by plaintext
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var strings_buf: [128][]const u8 = undefined;
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var strings_len: usize = 0;
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if (ad) |a| {
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strings_buf[strings_len] = a;
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strings_len += 1;
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}
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if (nonce) |n| {
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strings_buf[strings_len] = n;
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strings_len += 1;
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}
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strings_buf[strings_len] = m;
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strings_len += 1;
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// Verify synthetic IV using S2V
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var computed_tag: [tag_length]u8 = undefined;
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s2v(&computed_tag, k1.*, strings_buf[0..strings_len]);
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// Verify tag
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const verify = crypto.timing_safe.eql([tag_length]u8, computed_tag, tag);
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if (!verify) {
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crypto.secureZero(u8, &computed_tag);
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@memset(m, undefined);
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return error.AuthenticationFailed;
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}
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}
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/// Encrypts plaintext with multiple associated data components.
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/// This is the most general form of AES-SIV encryption that accepts
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/// an arbitrary vector of associated data strings as specified in RFC 5297.
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pub fn encryptWithAdVector(c: []u8, tag: *[tag_length]u8, m: []const u8, ad: []const []const u8, key: [key_length]u8) void {
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debug.assert(c.len == m.len);
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// Split key into K1 (for S2V) and K2 (for CTR)
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const k1 = key[0 .. Aes.key_bits / 8];
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const k2 = key[Aes.key_bits / 8 ..];
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// Prepare strings for S2V: AD components followed by plaintext
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var strings_buf: [128][]const u8 = undefined;
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var strings_len: usize = 0;
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for (ad) |a| {
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strings_buf[strings_len] = a;
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strings_len += 1;
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}
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strings_buf[strings_len] = m;
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strings_len += 1;
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// Compute synthetic IV using S2V
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s2v(tag, k1.*, strings_buf[0..strings_len]);
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// Clear the 31st and 63rd bits for use as CTR IV
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var ctr_iv = tag.*;
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ctr_iv[8] &= 0x7f;
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ctr_iv[12] &= 0x7f;
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// Encrypt plaintext using CTR mode
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const aes_ctx = Aes.initEnc(k2.*);
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modes.ctr(@TypeOf(aes_ctx), aes_ctx, c, m, ctr_iv, .big);
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}
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/// Decrypts ciphertext with multiple associated data components.
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/// This is the most general form of AES-SIV decryption that accepts
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/// an arbitrary vector of associated data strings as specified in RFC 5297.
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pub fn decryptWithAdVector(m: []u8, c: []const u8, tag: [tag_length]u8, ad: []const []const u8, key: [key_length]u8) AuthenticationError!void {
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assert(c.len == m.len);
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// Split key into K1 (for S2V) and K2 (for CTR)
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const k1 = key[0 .. Aes.key_bits / 8];
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const k2 = key[Aes.key_bits / 8 ..];
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// Clear the 31st and 63rd bits for use as CTR IV
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var ctr_iv = tag;
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ctr_iv[8] &= 0x7f;
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ctr_iv[12] &= 0x7f;
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// Decrypt ciphertext using CTR mode
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const aes_ctx = Aes.initEnc(k2.*);
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modes.ctr(@TypeOf(aes_ctx), aes_ctx, m, c, ctr_iv, .big);
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// Prepare strings for S2V: AD components followed by plaintext
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var strings_buf: [128][]const u8 = undefined;
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var strings_len: usize = 0;
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for (ad) |a| {
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strings_buf[strings_len] = a;
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strings_len += 1;
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}
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strings_buf[strings_len] = m;
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strings_len += 1;
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// Verify synthetic IV using S2V
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var computed_tag: [tag_length]u8 = undefined;
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s2v(&computed_tag, k1.*, strings_buf[0..strings_len]);
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// Verify tag
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const verify = crypto.timing_safe.eql([tag_length]u8, computed_tag, tag);
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if (!verify) {
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crypto.secureZero(u8, &computed_tag);
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@memset(m, undefined);
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return error.AuthenticationFailed;
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}
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}
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};
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}
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const htest = @import("test.zig");
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const testing = std.testing;
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test "AES-SIV double operation" {
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const AesSivTest = AesSiv(crypto.core.aes.Aes128);
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// Test vector from RFC 5297
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const input = [_]u8{ 0x0e, 0x04, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e };
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const expected = [_]u8{ 0x1c, 0x08, 0x02, 0x04, 0x06, 0x08, 0x0a, 0x0c, 0x0e, 0x10, 0x12, 0x14, 0x16, 0x18, 0x1a, 0x1c };
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const result = AesSivTest.dbl(input);
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try testing.expectEqualSlices(u8, &expected, &result);
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}
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test "AES-SIV double operation with MSB set" {
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const AesSivTest = AesSiv(crypto.core.aes.Aes128);
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const input = [_]u8{ 0xe0, 0x40, 0x10, 0x20, 0x30, 0x40, 0x50, 0x60, 0x70, 0x80, 0x90, 0xa0, 0xb0, 0xc0, 0xd0, 0xe0 };
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const expected = [_]u8{ 0xc0, 0x80, 0x20, 0x40, 0x60, 0x80, 0xa0, 0xc0, 0xe1, 0x01, 0x21, 0x41, 0x61, 0x81, 0xa1, 0x47 };
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const result = AesSivTest.dbl(input);
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try testing.expectEqualSlices(u8, &expected, &result);
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}
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test "Aes128Siv - RFC 5297 Test Vector A.1" {
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// Test vector from RFC 5297 Appendix A.1
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const key = [_]u8{
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0xff, 0xfe, 0xfd, 0xfc, 0xfb, 0xfa, 0xf9, 0xf8, 0xf7, 0xf6, 0xf5, 0xf4, 0xf3, 0xf2, 0xf1, 0xf0,
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0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
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};
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const ad = [_]u8{
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0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
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0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
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};
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const plaintext = [_]u8{
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0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee,
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};
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var ciphertext: [plaintext.len]u8 = undefined;
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var tag: [16]u8 = undefined;
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// Test using vector API for RFC compliance
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const ad_components = [_][]const u8{&ad};
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Aes128Siv.encryptWithAdVector(&ciphertext, &tag, &plaintext, &ad_components, key);
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// Expected values from RFC 5297
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try htest.assertEqual("85632d07c6e8f37f950acd320a2ecc93", &tag);
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try htest.assertEqual("40c02b9690c4dc04daef7f6afe5c", &ciphertext);
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// Test decryption
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var decrypted: [plaintext.len]u8 = undefined;
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try Aes128Siv.decryptWithAdVector(&decrypted, &ciphertext, tag, &ad_components, key);
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try testing.expectEqualSlices(u8, &plaintext, &decrypted);
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}
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test "Aes128Siv - RFC 5297 Test Vector A.2" {
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// Test vector from RFC 5297 Appendix A.2
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const key: [32]u8 = .{
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0x7f, 0x7e, 0x7d, 0x7c, 0x7b, 0x7a, 0x79, 0x78,
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0x77, 0x76, 0x75, 0x74, 0x73, 0x72, 0x71, 0x70,
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0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47,
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0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
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};
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const ad1 = [_]u8{
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0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77,
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0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff,
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0xde, 0xad, 0xda, 0xda, 0xde, 0xad, 0xda, 0xda,
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0xff, 0xee, 0xdd, 0xcc, 0xbb, 0xaa, 0x99, 0x88,
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0x77, 0x66, 0x55, 0x44, 0x33, 0x22, 0x11, 0x00,
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};
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const ad2 = [_]u8{
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0x10, 0x20, 0x30, 0x40, 0x50, 0x60, 0x70, 0x80,
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0x90, 0xa0,
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};
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const nonce: [16]u8 = .{
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0x09, 0xf9, 0x11, 0x02, 0x9d, 0x74, 0xe3, 0x5b,
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0xd8, 0x41, 0x56, 0xc5, 0x63, 0x56, 0x88, 0xc0,
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};
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const plaintext = [_]u8{
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0x74, 0x68, 0x69, 0x73, 0x20, 0x69, 0x73, 0x20,
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0x73, 0x6f, 0x6d, 0x65, 0x20, 0x70, 0x6c, 0x61,
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0x69, 0x6e, 0x74, 0x65, 0x78, 0x74, 0x20, 0x74,
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0x6f, 0x20, 0x65, 0x6e, 0x63, 0x72, 0x79, 0x70,
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0x74, 0x20, 0x75, 0x73, 0x69, 0x6e, 0x67, 0x20,
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0x53, 0x49, 0x56, 0x2d, 0x41, 0x45, 0x53,
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};
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var ciphertext: [plaintext.len]u8 = undefined;
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var tag: [16]u8 = undefined;
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Aes128Siv.encryptWithAdVector(&ciphertext, &tag, &plaintext, &.{ &ad1, &ad2, &nonce }, key);
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// Expected values from RFC 5297
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try htest.assertEqual("7bdb6e3b432667eb06f4d14bff2fbd0f", &tag);
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try htest.assertEqual("cb900f2fddbe404326601965c889bf17dba77ceb094fa663b7a3f748ba8af829ea64ad544a272e9c485b62a3fd5c0d", &ciphertext);
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}
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test "Aes128Siv - empty plaintext" {
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const key: [32]u8 = @splat(0x42);
|
|
const plaintext = "";
|
|
const ad = "additional data";
|
|
|
|
var ciphertext: [plaintext.len]u8 = undefined;
|
|
var tag: [16]u8 = undefined;
|
|
|
|
Aes128Siv.encrypt(&ciphertext, &tag, plaintext, ad, null, key);
|
|
|
|
var decrypted: [plaintext.len]u8 = undefined;
|
|
try Aes128Siv.decrypt(&decrypted, &ciphertext, tag, ad, null, key);
|
|
}
|
|
|
|
test "Aes128Siv - with nonce" {
|
|
const key: [32]u8 = @splat(0x69);
|
|
const nonce: [16]u8 = @splat(0x42);
|
|
const plaintext = "Hello, AES-SIV!";
|
|
const ad = "metadata";
|
|
|
|
var ciphertext: [plaintext.len]u8 = undefined;
|
|
var tag: [16]u8 = undefined;
|
|
|
|
Aes128Siv.encrypt(&ciphertext, &tag, plaintext, ad, &nonce, key);
|
|
|
|
var decrypted: [plaintext.len]u8 = undefined;
|
|
try Aes128Siv.decrypt(&decrypted, &ciphertext, tag, ad, &nonce, key);
|
|
try testing.expectEqualSlices(u8, plaintext, &decrypted);
|
|
}
|
|
|
|
test "Aes256Siv - basic functionality" {
|
|
const key: [64]u8 = @splat(0x96);
|
|
const plaintext = "Test message for AES-256-SIV";
|
|
const ad1 = "header";
|
|
const ad2 = "more data";
|
|
|
|
var ciphertext: [plaintext.len]u8 = undefined;
|
|
var tag: [16]u8 = undefined;
|
|
|
|
// Test with multiple AD components using the vector API
|
|
const ad_components = [_][]const u8{ ad1, ad2 };
|
|
Aes256Siv.encryptWithAdVector(&ciphertext, &tag, plaintext, &ad_components, key);
|
|
|
|
var decrypted: [plaintext.len]u8 = undefined;
|
|
try Aes256Siv.decryptWithAdVector(&decrypted, &ciphertext, tag, &ad_components, key);
|
|
try testing.expectEqualSlices(u8, plaintext, &decrypted);
|
|
}
|
|
|
|
test "Aes128Siv - demonstrating optional parameters" {
|
|
const key: [32]u8 = @splat(0x77);
|
|
|
|
// Test 1: No AD, no nonce (pure deterministic)
|
|
{
|
|
const plaintext = "Deterministic encryption";
|
|
var ciphertext: [plaintext.len]u8 = undefined;
|
|
var tag: [16]u8 = undefined;
|
|
|
|
Aes128Siv.encrypt(&ciphertext, &tag, plaintext, null, null, key);
|
|
|
|
var decrypted: [plaintext.len]u8 = undefined;
|
|
try Aes128Siv.decrypt(&decrypted, &ciphertext, tag, null, null, key);
|
|
try testing.expectEqualSlices(u8, plaintext, &decrypted);
|
|
}
|
|
|
|
// Test 2: With AD, no nonce
|
|
{
|
|
const plaintext = "With associated data";
|
|
const ad = "some context";
|
|
var ciphertext: [plaintext.len]u8 = undefined;
|
|
var tag: [16]u8 = undefined;
|
|
|
|
Aes128Siv.encrypt(&ciphertext, &tag, plaintext, ad, null, key);
|
|
|
|
var decrypted: [plaintext.len]u8 = undefined;
|
|
try Aes128Siv.decrypt(&decrypted, &ciphertext, tag, ad, null, key);
|
|
try testing.expectEqualSlices(u8, plaintext, &decrypted);
|
|
}
|
|
|
|
// Test 3: No AD, with nonce
|
|
{
|
|
const plaintext = "Nonce-based encryption";
|
|
const nonce: [12]u8 = @splat(0x01);
|
|
var ciphertext: [plaintext.len]u8 = undefined;
|
|
var tag: [16]u8 = undefined;
|
|
|
|
Aes128Siv.encrypt(&ciphertext, &tag, plaintext, null, &nonce, key);
|
|
|
|
var decrypted: [plaintext.len]u8 = undefined;
|
|
try Aes128Siv.decrypt(&decrypted, &ciphertext, tag, null, &nonce, key);
|
|
try testing.expectEqualSlices(u8, plaintext, &decrypted);
|
|
}
|
|
|
|
// Test 4: With both AD and nonce
|
|
{
|
|
const plaintext = "Full featured";
|
|
const ad = "context";
|
|
const nonce: [16]u8 = @splat(0x02);
|
|
var ciphertext: [plaintext.len]u8 = undefined;
|
|
var tag: [16]u8 = undefined;
|
|
|
|
Aes128Siv.encrypt(&ciphertext, &tag, plaintext, ad, &nonce, key);
|
|
|
|
var decrypted: [plaintext.len]u8 = undefined;
|
|
try Aes128Siv.decrypt(&decrypted, &ciphertext, tag, ad, &nonce, key);
|
|
try testing.expectEqualSlices(u8, plaintext, &decrypted);
|
|
}
|
|
}
|
|
|
|
test "Aes128Siv - authentication failure" {
|
|
const key: [32]u8 = @splat(0x13);
|
|
const plaintext = "Secret message";
|
|
const ad = "";
|
|
|
|
var ciphertext: [plaintext.len]u8 = undefined;
|
|
var tag: [16]u8 = undefined;
|
|
|
|
Aes128Siv.encrypt(&ciphertext, &tag, plaintext, ad, null, key);
|
|
|
|
// Corrupt the tag
|
|
tag[0] ^= 0x01;
|
|
|
|
var decrypted: [plaintext.len]u8 = undefined;
|
|
try testing.expectError(error.AuthenticationFailed, Aes128Siv.decrypt(&decrypted, &ciphertext, tag, ad, null, key));
|
|
}
|