tiny.reticulum.crypto.cbc

1const std = @import("std");23pub const block_length: u8 = 16;4pub const max_input_length: u16 = 65_520;56pub const CbcError = error{7    InputTooLong,8    InvalidLength,9    OutputTooSmall,10    OverlappingBuffers,11};1213/// AES-128 in cipher block chaining mode for the sealed message format this14/// package encrypts into (*token*) under a 32-byte key, following15/// Reticulum@1.5.0 RNS/Cryptography/AES.py:43-76.16pub const Aes128Cbc = Cbc(std.crypto.core.aes.Aes128);17/// AES-256 in cipher block chaining mode for the sealed message format this18/// package encrypts into (*token*) under a 64-byte key, following19/// Reticulum@1.5.0 RNS/Cryptography/AES.py:78-111.20pub const Aes256Cbc = Cbc(std.crypto.core.aes.Aes256);2122fn Cbc(comptime Cipher: type) type {23    return struct {24        pub const Key = [Cipher.key_bits / 8]u8;2526        pub fn encrypt(27            key: Key,28            iv: [block_length]u8,29            plaintext: []const u8,30            out: []u8,31        ) CbcError![]u8 {32            const result = try checkedOutput(plaintext, out);33            const cipher = Cipher.initEnc(key);34            var chain = iv;35            var offset: usize = 0;36            while (offset < plaintext.len) : (offset += block_length) {37                var block = plaintext[offset..][0..block_length].*;38                xor(&block, chain);39                cipher.encrypt(result[offset..][0..block_length], &block);40                chain = result[offset..][0..block_length].*;41            }42            return result;43        }4445        pub fn decrypt(46            key: Key,47            iv: [block_length]u8,48            ciphertext: []const u8,49            out: []u8,50        ) CbcError![]u8 {51            const result = try checkedOutput(ciphertext, out);52            const cipher = Cipher.initDec(key);53            var chain = iv;54            var offset: usize = 0;55            while (offset < ciphertext.len) : (offset += block_length) {56                const encrypted = ciphertext[offset..][0..block_length].*;57                var block: [block_length]u8 = undefined;58                cipher.decrypt(&block, &encrypted);59                xor(&block, chain);60                result[offset..][0..block_length].* = block;61                chain = encrypted;62            }63            return result;64        }65    };66}6768fn checkedOutput(input: []const u8, out: []u8) CbcError![]u8 {69    if (input.len > max_input_length) return error.InputTooLong;70    if (input.len % block_length != 0) return error.InvalidLength;71    if (out.len < input.len) return error.OutputTooSmall;72    const result = out[0..input.len];73    if (partiallyOverlaps(input, result)) return error.OverlappingBuffers;74    return result;75}7677fn partiallyOverlaps(input: []const u8, output: []u8) bool {78    if (input.len == 0) return false;79    const input_start = @intFromPtr(input.ptr);80    const output_start = @intFromPtr(output.ptr);81    if (input_start == output_start) return false;82    const input_end = input_start + input.len;83    const output_end = output_start + output.len;84    return input_start < output_end and output_start < input_end;85}8687fn xor(block: *[block_length]u8, chain: [block_length]u8) void {88    for (block, chain) |*byte, previous| byte.* ^= previous;89}

1pub const cbc = @import("cbc.zig");