RC6

RC6 proper has a block size of 128 bits and supports key sizes of 128, 192, and 256 bits up to 2040-bits, but, like RC5, it may be parameterised to support a wide variety of word-lengths, key sizes, and number of rounds. RC6 is very similar to RC5 in structure, using data-dependent rotations, modular addition, and XOR operations; in fact, RC6 could be viewed as interweaving two parallel RC5 encryption processes, although RC6 does use an extra multiplication operation not present in RC5 in order to make the rotation dependent on every bit in a word, and not just the least significant few bits.

Encryption/decryption

The key expansion algorithm is practically identical to that of RC5. The only difference is that for RC6, more words are derived from the user-supplied key.

<span id="mwKA"></span><span class="c1" id="mwKQ">// Encryption/Decryption with RC6-w/r/b</span> <span class="c1" id="mwKg">// </span> <span class="c1" id="mwKw">// Input: Plaintext stored in four w-bit input registers A, B, C & D</span> <span class="c1" id="mwLA">// r is the number of rounds</span> <span class="c1" id="mwLQ">// w-bit round keys S[0, ... , 2r + 3]</span> <span class="c1" id="mwLg">// </span> <span class="c1" id="mwLw">// Output: Ciphertext stored in A, B, C, D</span> <span class="c1" id="mwMA">// </span> <span class="c1" id="mwMQ">// '''Encryption Procedure:'''</span> <span class="w" id="mwMg"> </span><span class="n" id="mwMw">B</span><span class="w" id="mwNA"> </span><span class="o" id="mwNQ">=</span><span class="w" id="mwNg"> </span><span class="n" id="mwNw">B</span><span class="w" id="mwOA"> </span><span class="o" id="mwOQ">+</span><span class="w" id="mwOg"> </span><span class="n" id="mwOw">S</span><span class="p" id="mwPA">[</span><span class="mi" id="mwPQ">0</span><span class="p" id="mwPg">]</span> <span class="w" id="mwPw"> </span><span class="n" id="mwQA">D</span><span class="w" id="mwQQ"> </span><span class="o" id="mwQg">=</span><span class="w" id="mwQw"> </span><span class="n" id="mwRA">D</span><span class="w" id="mwRQ"> </span><span class="o" id="mwRg">+</span><span class="w" id="mwRw"> </span><span class="n" id="mwSA">S</span><span class="p" id="mwSQ">[</span><span class="mi" id="mwSg">1</span><span class="p" id="mwSw">]</span> <span class="w" id="mwTA"> </span><span class="k" id="mwTQ">for</span><span class="w" id="mwTg"> </span><span class="n" id="mwTw">i</span><span class="w" id="mwUA"> </span><span class="o" id="mwUQ">=</span><span class="w" id="mwUg"> </span><span class="mi" id="mwUw">1</span><span class="w" id="mwVA"> </span><span class="n" id="mwVQ">to</span><span class="w" id="mwVg"> </span><span class="n" id="mwVw">r</span><span class="w" id="mwWA"> </span><span class="k" id="mwWQ">do</span> <span class="w" id="mwWg"> </span><span class="p" id="mwWw">{</span> <span class="w" id="mwXA"> </span><span class="n" id="mwXQ">t</span><span class="w" id="mwXg"> </span><span class="o" id="mwXw">=</span><span class="w" id="mwYA"> </span><span class="p" id="mwYQ">(</span><span class="n" id="mwYg">B</span><span class="w" id="mwYw"> </span><span class="o" id="mwZA">*</span><span class="w" id="mwZQ"> </span><span class="p" id="mwZg">(</span><span class="mi" id="mwZw">2</span><span class="n" id="mwaA">B</span><span class="w" id="mwaQ"> </span><span class="o" id="mwag">+</span><span class="w" id="mwaw"> </span><span class="mi" id="mwbA">1</span><span class="p" id="mwbQ">))</span><span class="w" id="mwbg"> </span><span class="o" id="mwbw"><<<</span><span class="w" id="mwcA"> </span><span class="n" id="mwcQ">lg</span><span class="w" id="mwcg"> </span><span class="n" id="mwcw">w</span> <span class="w" id="mwdA"> </span><span class="n" id="mwdQ">u</span><span class="w" id="mwdg"> </span><span class="o" id="mwdw">=</span><span class="w" id="mweA"> </span><span class="p" id="mweQ">(</span><span class="n" id="mweg">D</span><span class="w" id="mwew"> </span><span class="o" id="mwfA">*</span><span class="w" id="mwfQ"> </span><span class="p" id="mwfg">(</span><span class="mi" id="mwfw">2</span><span class="n" id="mwgA">D</span><span class="w" id="mwgQ"> </span><span class="o" id="mwgg">+</span><span class="w" id="mwgw"> </span><span class="mi" id="mwhA">1</span><span class="p" id="mwhQ">))</span><span class="w" id="mwhg"> </span><span class="o" id="mwhw"><<<</span><span class="w" id="mwiA"> </span><span class="n" id="mwiQ">lg</span><span class="w" id="mwig"> </span><span class="n" id="mwiw">w</span> <span class="w" id="mwjA"> </span><span class="n" id="mwjQ">A</span><span class="w" id="mwjg"> </span><span class="o" id="mwjw">=</span><span class="w" id="mwkA"> </span><span class="p" id="mwkQ">((</span><span class="n" id="mwkg">A</span><span class="w" id="mwkw"> </span><span class="o" id="mwlA">^</span><span class="w" id="mwlQ"> </span><span class="n" id="mwlg">t</span><span class="p" id="mwlw">)</span><span class="w" id="mwmA"> </span><span class="o" id="mwmQ"><<<</span><span class="w" id="mwmg"> </span><span class="n" id="mwmw">u</span><span class="p" id="mwnA">)</span><span class="w" id="mwnQ"> </span><span class="o" id="mwng">+</span><span class="w" id="mwnw"> </span><span class="n" id="mwoA">S</span><span class="p" id="mwoQ">[</span><span class="mi" id="mwog">2</span><span class="n" id="mwow">i</span><span class="p" id="mwpA">]</span> <span class="w" id="mwpQ"> </span><span class="n" id="mwpg">C</span><span class="w" id="mwpw"> </span><span class="o" id="mwqA">=</span><span class="w" id="mwqQ"> </span><span class="p" id="mwqg">((</span><span class="n" id="mwqw">C</span><span class="w" id="mwrA"> </span><span class="o" id="mwrQ">^</span><span class="w" id="mwrg"> </span><span class="n" id="mwrw">u</span><span class="p" id="mwsA">)</span><span class="w" id="mwsQ"> </span><span class="o" id="mwsg"><<<</span><span class="w" id="mwsw"> </span><span class="n" id="mwtA">t</span><span class="p" id="mwtQ">)</span><span class="w" id="mwtg"> </span><span class="o" id="mwtw">+</span><span class="w" id="mwuA"> </span><span class="n" id="mwuQ">S</span><span class="p" id="mwug">[</span><span class="mi" id="mwuw">2</span><span class="n" id="mwvA">i</span><span class="w" id="mwvQ"> </span><span class="o" id="mwvg">+</span><span class="w" id="mwvw"> </span><span class="mi" id="mwwA">1</span><span class="p" id="mwwQ">]</span><span class="w" id="mwwg"> </span> <span class="w" id="mwww"> </span><span class="p" id="mwxA">(</span><span class="n" id="mwxQ">A</span><span class="p" id="mwxg">,</span><span class="w" id="mwxw"> </span><span class="n" id="mwyA">B</span><span class="p" id="mwyQ">,</span><span class="w" id="mwyg"> </span><span class="n" id="mwyw">C</span><span class="p" id="mwzA">,</span><span class="w" id="mwzQ"> </span><span class="n" id="mwzg">D</span><span class="p" id="mwzw">)</span><span class="w" id="mw0A"> </span><span class="o" id="mw0Q">=</span><span class="w" id="mw0g"> </span><span class="p" id="mw0w">(</span><span class="n" id="mw1A">B</span><span class="p" id="mw1Q">,</span><span class="w" id="mw1g"> </span><span class="n" id="mw1w">C</span><span class="p" id="mw2A">,</span><span class="w" id="mw2Q"> </span><span class="n" id="mw2g">D</span><span class="p" id="mw2w">,</span><span class="w" id="mw3A"> </span><span class="n" id="mw3Q">A</span><span class="p" id="mw3g">)</span> <span class="w" id="mw3w"> </span><span class="p" id="mw4A">}</span> <span class="w" id="mw4Q"> </span><span class="n" id="mw4g">A</span><span class="w" id="mw4w"> </span><span class="o" id="mw5A">=</span><span class="w" id="mw5Q"> </span><span class="n" id="mw5g">A</span><span class="w" id="mw5w"> </span><span class="o" id="mw6A">+</span><span class="w" id="mw6Q"> </span><span class="n" id="mw6g">S</span><span class="p" id="mw6w">[</span><span class="mi" id="mw7A">2</span><span class="n" id="mw7Q">r</span><span class="w" id="mw7g"> </span><span class="o" id="mw7w">+</span><span class="w" id="mw8A"> </span><span class="mi" id="mw8Q">2</span><span class="p" id="mw8g">]</span> <span class="w" id="mw8w"> </span><span class="n" id="mw9A">C</span><span class="w" id="mw9Q"> </span><span class="o" id="mw9g">=</span><span class="w" id="mw9w"> </span><span class="n" id="mw-A">C</span><span class="w" id="mw-Q"> </span><span class="o" id="mw-g">+</span><span class="w" id="mw-w"> </span><span class="n" id="mw_A">S</span><span class="p" id="mw_Q">[</span><span class="mi" id="mw_g">2</span><span class="n" id="mw_w">r</span><span class="w" id="mwAQA"> </span><span class="o" id="mwAQE">+</span><span class="w" id="mwAQI"> </span><span class="mi" id="mwAQM">3</span><span class="p" id="mwAQQ">]</span> <span class="c1" id="mwAQU">// '''Decryption Procedure:'''</span> <span class="w" id="mwAQY"> </span><span class="n" id="mwAQc">C</span><span class="w" id="mwAQg"> </span><span class="o" id="mwAQk">=</span><span class="w" id="mwAQo"> </span><span class="n" id="mwAQs">C</span><span class="w" id="mwAQw"> </span><span class="o" id="mwAQ0">-</span><span class="w" id="mwAQ4"> </span><span class="n" id="mwAQ8">S</span><span class="p" id="mwARA">[</span><span class="mi" id="mwARE">2</span><span class="n" id="mwARI">r</span><span class="w" id="mwARM"> </span><span class="o" id="mwARQ">+</span><span class="w" id="mwARU"> </span><span class="mi" id="mwARY">3</span><span class="p" id="mwARc">]</span> <span class="w" id="mwARg"> </span><span class="n" id="mwARk">A</span><span class="w" id="mwARo"> </span><span class="o" id="mwARs">=</span><span class="w" id="mwARw"> </span><span class="n" id="mwAR0">A</span><span class="w" id="mwAR4"> </span><span class="o" id="mwAR8">-</span><span class="w" id="mwASA"> </span><span class="n" id="mwASE">S</span><span class="p" id="mwASI">[</span><span class="mi" id="mwASM">2</span><span class="n" id="mwASQ">r</span><span class="w" id="mwASU"> </span><span class="o" id="mwASY">+</span><span class="w" id="mwASc"> </span><span class="mi" id="mwASg">2</span><span class="p" id="mwASk">]</span> <span class="w" id="mwASo"> </span><span class="k" id="mwASs">for</span><span class="w" id="mwASw"> </span><span class="n" id="mwAS0">i</span><span class="w" id="mwAS4"> </span><span class="o" id="mwAS8">=</span><span class="w" id="mwATA"> </span><span class="n" id="mwATE">r</span><span class="w" id="mwATI"> </span><span class="n" id="mwATM">downto</span><span class="w" id="mwATQ"> </span><span class="mi" id="mwATU">1</span><span class="w" id="mwATY"> </span><span class="k" id="mwATc">do</span> <span class="w" id="mwATg"> </span><span class="p" id="mwATk">{</span> <span class="w" id="mwATo"> </span><span class="p" id="mwATs">(</span><span class="n" id="mwATw">A</span><span class="p" id="mwAT0">,</span><span class="w" id="mwAT4"> </span><span class="n" id="mwAT8">B</span><span class="p" id="mwAUA">,</span><span class="w" id="mwAUE"> </span><span class="n" id="mwAUI">C</span><span class="p" id="mwAUM">,</span><span class="w" id="mwAUQ"> </span><span class="n" id="mwAUU">D</span><span class="p" id="mwAUY">)</span><span class="w" id="mwAUc"> </span><span class="o" id="mwAUg">=</span><span class="w" id="mwAUk"> </span><span class="p" id="mwAUo">(</span><span class="n" id="mwAUs">D</span><span class="p" id="mwAUw">,</span><span class="w" id="mwAU0"> </span><span class="n" id="mwAU4">A</span><span class="p" id="mwAU8">,</span><span class="w" id="mwAVA"> </span><span class="n" id="mwAVE">B</span><span class="p" id="mwAVI">,</span><span class="w" id="mwAVM"> </span><span class="n" id="mwAVQ">C</span><span class="p" id="mwAVU">)</span> <span class="w" id="mwAVY"> </span><span class="n" id="mwAVc">u</span><span class="w" id="mwAVg"> </span><span class="o" id="mwAVk">=</span><span class="w" id="mwAVo"> </span><span class="p" id="mwAVs">(</span><span class="n" id="mwAVw">D</span><span class="w" id="mwAV0"> </span><span class="o" id="mwAV4">*</span><span class="w" id="mwAV8"> </span><span class="p" id="mwAWA">(</span><span class="mi" id="mwAWE">2</span><span class="n" id="mwAWI">D</span><span class="w" id="mwAWM"> </span><span class="o" id="mwAWQ">+</span><span class="w" id="mwAWU"> </span><span class="mi" id="mwAWY">1</span><span class="p" id="mwAWc">))</span><span class="w" id="mwAWg"> </span><span class="o" id="mwAWk"><<<</span><span class="w" id="mwAWo"> </span><span class="n" id="mwAWs">lg</span><span class="w" id="mwAWw"> </span><span class="n" id="mwAW0">w</span> <span class="w" id="mwAW4"> </span><span class="n" id="mwAW8">t</span><span class="w" id="mwAXA"> </span><span class="o" id="mwAXE">=</span><span class="w" id="mwAXI"> </span><span class="p" id="mwAXM">(</span><span class="n" id="mwAXQ">B</span><span class="w" id="mwAXU"> </span><span class="o" id="mwAXY">*</span><span class="w" id="mwAXc"> </span><span class="p" id="mwAXg">(</span><span class="mi" id="mwAXk">2</span><span class="n" id="mwAXo">B</span><span class="w" id="mwAXs"> </span><span class="o" id="mwAXw">+</span><span class="w" id="mwAX0"> </span><span class="mi" id="mwAX4">1</span><span class="p" id="mwAX8">))</span><span class="w" id="mwAYA"> </span><span class="o" id="mwAYE"><<<</span><span class="w" id="mwAYI"> </span><span class="n" id="mwAYM">lg</span><span class="w" id="mwAYQ"> </span><span class="n" id="mwAYU">w</span> <span class="w" id="mwAYY"> </span><span class="n" id="mwAYc">C</span><span class="w" id="mwAYg"> </span><span class="o" id="mwAYk">=</span><span class="w" id="mwAYo"> </span><span class="p" id="mwAYs">((</span><span class="n" id="mwAYw">C</span><span class="w" id="mwAY0"> </span><span class="o" id="mwAY4">-</span><span class="w" id="mwAY8"> </span><span class="n" id="mwAZA">S</span><span class="p" id="mwAZE">[</span><span class="mi" id="mwAZI">2</span><span class="n" id="mwAZM">i</span><span class="w" id="mwAZQ"> </span><span class="o" id="mwAZU">+</span><span class="w" id="mwAZY"> </span><span class="mi" id="mwAZc">1</span><span class="p" id="mwAZg">])</span><span class="w" id="mwAZk"> </span><span class="o" id="mwAZo">>>></span><span class="w" id="mwAZs"> </span><span class="n" id="mwAZw">t</span><span class="p" id="mwAZ0">)</span><span class="w" id="mwAZ4"> </span><span class="o" id="mwAZ8">^</span><span class="w" id="mwAaA"> </span><span class="n" id="mwAaE">u</span> <span class="w" id="mwAaI"> </span><span class="n" id="mwAaM">A</span><span class="w" id="mwAaQ"> </span><span class="o" id="mwAaU">=</span><span class="w" id="mwAaY"> </span><span class="p" id="mwAac">((</span><span class="n" id="mwAag">A</span><span class="w" id="mwAak"> </span><span class="o" id="mwAao">-</span><span class="w" id="mwAas"> </span><span class="n" id="mwAaw">S</span><span class="p" id="mwAa0">[</span><span class="mi" id="mwAa4">2</span><span class="n" id="mwAa8">i</span><span class="p" id="mwAbA">])</span><span class="w" id="mwAbE"> </span><span class="o" id="mwAbI">>>></span><span class="w" id="mwAbM"> </span><span class="n" id="mwAbQ">u</span><span class="p" id="mwAbU">)</span><span class="w" id="mwAbY"> </span><span class="o" id="mwAbc">^</span><span class="w" id="mwAbg"> </span><span class="n" id="mwAbk">t</span> <span class="w" id="mwAbo"> </span><span class="p" id="mwAbs">}</span> <span class="w" id="mwAbw"> </span><span class="n" id="mwAb0">D</span><span class="w" id="mwAb4"> </span><span class="o" id="mwAb8">=</span><span class="w" id="mwAcA"> </span><span class="n" id="mwAcE">D</span><span class="w" id="mwAcI"> </span><span class="o" id="mwAcM">-</span><span class="w" id="mwAcQ"> </span><span class="n" id="mwAcU">S</span><span class="p" id="mwAcY">[</span><span class="mi" id="mwAcc">1</span><span class="p" id="mwAcg">]</span> <span class="w" id="mwAck"> </span><span class="n" id="mwAco">B</span><span class="w" id="mwAcs"> </span><span class="o" id="mwAcw">=</span><span class="w" id="mwAc0"> </span><span class="n" id="mwAc4">B</span><span class="w" id="mwAc8"> </span><span class="o" id="mwAdA">-</span><span class="w" id="mwAdE"> </span><span class="n" id="mwAdI">S</span><span class="p" id="mwAdM">[</span><span class="mi" id="mwAdQ">0</span><span class="p" id="mwAdU">]</span>