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README.md

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+# SHAmwow
+
+Sometimes you just want to understand how an algorithm works, so you implement it yourself.
+
+The sha2 function in shamwow.rb implements the SHA-256 hashing function in Ruby. shamwow_test.rb contains a few sanity tests for the right-rotate function and for SHA2 itself, testing against the output of the `Digest::SHA2.hexdigest` method in the Ruby standard library.
+
+It should go without saying that this was just for fun, and you should never, ever roll-your-own cryptography primatives for any reasonable purpose!
+
+This was fun.
+
+## Sources
+
+* the actual spec: <http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf>
+* wikipedia's pseudocode breakdown: <https://en.wikipedia.org/wiki/SHA-2#Pseudocode>
+* a JS implementation that helped as I was debugging some boneheaded mistakes: <http://www.movable-type.co.uk/scripts/sha256.html>
+
+## Obligatory
+
+<iframe width="560" height="315" src="https://www.youtube.com/embed/F3lrhPeK6gU" frameborder="0" allowfullscreen></iframe>

shamwow.rb

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+#!/usr/local/bin/ruby
+
+def chunker(string, chunk_size)
+  return (string.length / chunk_size).times.collect { |i| string[i * chunk_size, chunk_size] }
+end
+
+# treat all numbers as if they are 32-bit integers
+def ror(num, shift)
+  ((num >> shift) | (num << (32-shift)) & ((2 ** 32) - 1))
+end
+
+def sha2(message)
+  
+  # Implementation taken from https://en.wikipedia.org/wiki/SHA-2#Pseudocode
+  message_in_bits = message.unpack("B*")[0]
+  
+  # first 32 bits of the fractional parts of the square roots of the first 8 primes 2 through 19:
+  h0 = 0x6a09e667
+  h1 = 0xbb67ae85
+  h2 = 0x3c6ef372
+  h3 = 0xa54ff53a
+  h4 = 0x510e527f
+  h5 = 0x9b05688c
+  h6 = 0x1f83d9ab
+  h7 = 0x5be0cd19
+
+  # first 32 bits of the fractional parts of the cube roots of the first 64 primes 2 through 311:
+  k = [
+      0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
+      0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
+      0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
+      0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
+      0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
+      0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
+      0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
+      0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
+    ]
+
+  len = message_in_bits.length
+  bits = message_in_bits
+  bits << "1"
+  bits << "0" * (512 - ((bits.length + 64) % 512))
+  bits << "%064b" % len
+
+  chunked = chunker(bits, 512)
+
+  i = 0
+  while i < chunked.length
+    m = []
+
+    message = chunker(chunked[i], 32)
+    message.each_with_index { |word, index| m[index] = word.to_i(2) } # here's where we pass from strings of 1s and 0s back to numbers
+
+    (16..63).each { |word|
+      s0 = ror(m[word-15], 7) ^ ror(m[word-15], 18) ^ (m[word-15] >> 3)
+      s1 = ror(m[word-2], 17) ^ ror(m[word-2],  19) ^ (m[word-2] >> 10)
+      m[word] = (m[word-16] + s0 + m[word-7] + s1) & 0xFFFFFFFF
+    }
+
+    a = h0
+    b = h1
+    c = h2
+    d = h3
+    e = h4
+    f = h5
+    g = h6
+    h = h7
+
+    (0..63).each { |word|
+      s1 = ror(e, 6) ^ ror(e, 11) ^ ror(e, 25)
+      ch = (e & f) ^ (~(e) & g)
+      temp1 = (h + s1 + ch + k[word] + m[word]) & 0xFFFFFFFF
+      s0 = ror(a, 2) ^ ror(a, 13) ^ ror(a, 22)
+      maj = (a & b) ^ (a & c) ^ (b & c)
+      temp2 = (s0 + maj) & 0xFFFFFFFF
+
+      h = g
+      g = f
+      f = e
+      e = (d + temp1) & 0xFFFFFFFF
+      d = c
+      c = b
+      b = a
+      a = (temp1 + temp2) & 0xFFFFFFFF
+    }
+
+    h0 = (h0 + a) & 0xFFFFFFFF
+    h1 = (h1 + b) & 0xFFFFFFFF
+    h2 = (h2 + c) & 0xFFFFFFFF
+    h3 = (h3 + d) & 0xFFFFFFFF
+    h4 = (h4 + e) & 0xFFFFFFFF
+    h5 = (h5 + f) & 0xFFFFFFFF
+    h6 = (h6 + g) & 0xFFFFFFFF
+    h7 = (h7 + h) & 0xFFFFFFFF
+
+    i = i + 1
+  end
+
+  ("%08x" % h0).concat("%08x" % h1).concat("%08x" % h2).concat("%08x" % h3).concat("%08x" % h4).concat("%08x" % h5).concat("%08x" % h6).concat("%08x" % h7)
+end

shamwow_test.rb

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+#!/usr/local/bin/ruby
+
+require_relative "shamwow"
+require "test/unit"
+require 'digest'
+ 
+class TestShamwow < Test::Unit::TestCase
+
+  def test_ror
+    assert_equal(0, ror(0, 0))
+    assert_equal(0x80000000, ror(1, 1))
+    assert_equal(0x80000001, ror(3, 1))
+    assert_equal("00111111111111111111111111111111".to_i(2), ror("01111111111111111111111111111110".to_i(2), 1))
+    assert_equal("01111111111111111111111111111111".to_i(2), ror("11111111111111111111111111111110".to_i(2), 1))
+    assert_equal("10111111111111110111111111111111".to_i(2), ror("11111111111111011111111111111110".to_i(2), 2))
+    assert_equal("11111111111111011111111111111110".to_i(2), ror("11111111111111011111111111111110".to_i(2), 32))
+    assert_equal("01111111111111111111111111111111".to_i(2), ror("11111111111111111111111111111110".to_i(2), 33))
+    assert_equal("11111111111111111111111111111110".to_i(2), ror("011111111111111111111111111111101".to_i(2), 1))
+  end
+
+  def test_sha2
+    assert_equal(Digest::SHA2.hexdigest('abc'), sha2("abc"))
+    assert_equal(Digest::SHA2.hexdigest("上一页"), sha2("上一页"))
+    assert_equal(Digest::SHA2.hexdigest("😀"), sha2("😀"))
+    assert_equal(Digest::SHA2.hexdigest("ЁЂЃЄЅІЇЈЉЊЋЌЍЎЏАБВГДЕЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯабвгдежзийклмнопрстуфхцчшщъыьэюя"), sha2("ЁЂЃЄЅІЇЈЉЊЋЌЍЎЏАБВГДЕЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯабвгдежзийклмнопрстуфхцчшщъыьэюя"))
+    assert_equal(Digest::SHA2.hexdigest("𝕿𝖍𝖊 𝖖𝖚𝖎𝖈𝖐 𝖇𝖗𝖔𝖜𝖓 𝖋𝖔𝖝 𝖏𝖚𝖒𝖕𝖘 𝖔𝖛𝖊𝖗 𝖙𝖍𝖊 𝖑𝖆𝖟𝖞 𝖉𝖔𝖌"), sha2("𝕿𝖍𝖊 𝖖𝖚𝖎𝖈𝖐 𝖇𝖗𝖔𝖜𝖓 𝖋𝖔𝖝 𝖏𝖚𝖒𝖕𝖘 𝖔𝖛𝖊𝖗 𝖙𝖍𝖊 𝖑𝖆𝖟𝖞 𝖉𝖔𝖌"))
+
+    preamble = "We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America."
+    assert_equal(Digest::SHA2.hexdigest(preamble), sha2(preamble))
+
+    gettysburg = "Four score and seven years ago our fathers brought forth on this continent, a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal. Now we are engaged in a great civil war, testing whether that nation, or any nation so conceived and so dedicated, can long endure. We are met on a great battle-field of that war. We have come to dedicate a portion of that field, as a final resting place for those who here gave their lives that that nation might live. It is altogether fitting and proper that we should do this. But, in a larger sense, we can not dedicate -- we can not consecrate -- we can not hallow -- this ground. The brave men, living and dead, who struggled here, have consecrated it, far above our poor power to add or detract. The world will little note, nor long remember what we say here, but it can never forget what they did here. It is for us the living, rather, to be dedicated here to the unfinished work which they who fought here have thus far so nobly advanced. It is rather for us to be here dedicated to the great task remaining before us -- that from these honored dead we take increased devotion to that cause for which they gave the last full measure of devotion -- that we here highly resolve that these dead shall not have died in vain -- that this nation, under God, shall have a new birth of freedom -- and that government of the people, by the people, for the people, shall not perish from the earth."
+    assert_equal(Digest::SHA2.hexdigest(gettysburg), sha2(gettysburg))
+  end
+
+end