SHA-256 implementation in Python

Question

I'm looking for a Python implementation of the SHA-256 hash function. I want to use it to get a better understanding of how the SHA-256 function works, and I think Python is the ideal language for this. Pseudo-code has the limitation that I can't run/test it, to see what my modifications of the code do to the output.

Answer 1

PyPy's source contains a pure-python implementation of SHA-256 here. Poking around in that directory, you'll probably also find pure-python implementations of other standard hashes.

Answer 2

initial_hash_values=[ '6a09e667','bb67ae85','3c6ef372','a54ff53a', '510e527f','9b05688c','1f83d9ab','5be0cd19' ]  sha_256_constants=[ '428a2f98','71374491','b5c0fbcf','e9b5dba5', '3956c25b','59f111f1','923f82a4','ab1c5ed5', 'd807aa98','12835b01','243185be','550c7dc3', '72be5d74','80deb1fe','9bdc06a7','c19bf174', 'e49b69c1','efbe4786','0fc19dc6','240ca1cc', '2de92c6f','4a7484aa','5cb0a9dc','76f988da', '983e5152','a831c66d','b00327c8','bf597fc7', 'c6e00bf3','d5a79147','06ca6351','14292967', '27b70a85','2e1b2138','4d2c6dfc','53380d13', '650a7354','766a0abb','81c2c92e','92722c85', 'a2bfe8a1','a81a664b','c24b8b70','c76c51a3', 'd192e819','d6990624','f40e3585','106aa070', '19a4c116','1e376c08','2748774c','34b0bcb5', '391c0cb3','4ed8aa4a','5b9cca4f','682e6ff3', '748f82ee','78a5636f','84c87814','8cc70208', '90befffa','a4506ceb','bef9a3f7','c67178f2' ]  def bin_return(dec):     return(str(format(dec,'b')))  def bin_8bit(dec):     return(str(format(dec,'08b')))  def bin_32bit(dec):     return(str(format(dec,'032b')))  def bin_64bit(dec):     return(str(format(dec,'064b')))  def hex_return(dec):     return(str(format(dec,'x')))  def dec_return_bin(bin_string):     return(int(bin_string,2))  def dec_return_hex(hex_string):     return(int(hex_string,16))  def L_P(SET,n):     to_return=[]     j=0     k=n     while k<len(SET)+1:         to_return.append(SET[j:k])         j=k         k+=n      return(to_return)  def s_l(bit_string):     bit_list=[]     for i in range(len(bit_string)):         bit_list.append(bit_string[i])     return(bit_list)  def l_s(bit_list):     bit_string=''     for i in range(len(bit_list)):         bit_string+=bit_list[i]     return(bit_string)  def rotate_right(bit_string,n):     bit_list = s_l(bit_string)     count=0     while count <= n-1:         list_main=list(bit_list)         var_0=list_main.pop(-1)         list_main=list([var_0]+list_main)         bit_list=list(list_main)         count+=1     return(l_s(list_main))  def shift_right(bit_string,n):     bit_list=s_l(bit_string)     count=0     while count <= n-1:         bit_list.pop(-1)         count+=1     front_append=['0']*n     return(l_s(front_append+bit_list))  def mod_32_addition(input_set):     value=0     for i in range(len(input_set)):         value+=input_set[i]     mod_32 = 4294967296     return(value%mod_32)  def xor_2str(bit_string_1,bit_string_2):     xor_list=[]     for i in range(len(bit_string_1)):         if bit_string_1[i]=='0' and bit_string_2[i]=='0':             xor_list.append('0')         if bit_string_1[i]=='1' and bit_string_2[i]=='1':             xor_list.append('0')         if bit_string_1[i]=='0' and bit_string_2[i]=='1':             xor_list.append('1')         if bit_string_1[i]=='1' and bit_string_2[i]=='0':             xor_list.append('1')     return(l_s(xor_list))  def and_2str(bit_string_1,bit_string_2):     and_list=[]     for i in range(len(bit_string_1)):         if bit_string_1[i]=='1' and bit_string_2[i]=='1':             and_list.append('1')         else:             and_list.append('0')                  return(l_s(and_list))  def or_2str(bit_string_1,bit_string_2):     or_list=[]     for i in range(len(bit_string_1)):         if bit_string_1[i]=='0' and bit_string_2[i]=='0':             or_list.append('0')         else:             or_list.append('1')     return(l_s(or_list))  def not_str(bit_string):     not_list=[]     for i in range(len(bit_string)):         if bit_string[i]=='0':             not_list.append('1')         else:             not_list.append('0')     return(l_s(not_list))  ''' SHA-256 Specific Functions: '''  def Ch(x,y,z):     return(xor_2str(and_2str(x,y),and_2str(not_str(x),z)))  def Maj(x,y,z):     return(xor_2str(xor_2str(and_2str(x,y),and_2str(x,z)),and_2str(y,z)))  def e_0(x):     return(xor_2str(xor_2str(rotate_right(x,2),rotate_right(x,13)),rotate_right(x,22)))  def e_1(x):     return(xor_2str(xor_2str(rotate_right(x,6),rotate_right(x,11)),rotate_right(x,25)))  def s_0(x):     return(xor_2str(xor_2str(rotate_right(x,7),rotate_right(x,18)),shift_right(x,3)))  def s_1(x):     return(xor_2str(xor_2str(rotate_right(x,17),rotate_right(x,19)),shift_right(x,10)))  def message_pad(bit_list):     pad_one = bit_list + '1'     pad_len = len(pad_one)     k=0     while ((pad_len+k)-448)%512 != 0:         k+=1     back_append_0 = '0'*k     back_append_1 = bin_64bit(len(bit_list))     return(pad_one+back_append_0+back_append_1)      def message_bit_return(string_input):     bit_list=[]     for i in range(len(string_input)):         bit_list.append(bin_8bit(ord(string_input[i])))     return(l_s(bit_list))  def message_pre_pro(input_string):     bit_main = message_bit_return(input_string)     return(message_pad(bit_main))  def message_parsing(input_string):     return(L_P(message_pre_pro(input_string),32))  def message_schedule(index,w_t):     new_word = bin_32bit(mod_32_addition([int(s_1(w_t[index-2]),2),int(w_t[index-7],2),int(s_0(w_t[index-15]),2),int(w_t[index-16],2)]))     return(new_word)  ''' This example of SHA_256 works for an input string <56 characters. '''  def sha_256(input_string):     assert len(input_string) < 56, "This example of SHA_256 works for an input string <56 characters."     w_t=message_parsing(input_string)     a=bin_32bit(dec_return_hex(initial_hash_values[0]))     b=bin_32bit(dec_return_hex(initial_hash_values[1]))     c=bin_32bit(dec_return_hex(initial_hash_values[2]))     d=bin_32bit(dec_return_hex(initial_hash_values[3]))     e=bin_32bit(dec_return_hex(initial_hash_values[4]))     f=bin_32bit(dec_return_hex(initial_hash_values[5]))     g=bin_32bit(dec_return_hex(initial_hash_values[6]))     h=bin_32bit(dec_return_hex(initial_hash_values[7]))     for i in range(0,64):         if i <= 15:              t_1=mod_32_addition([int(h,2),int(e_1(e),2),int(Ch(e,f,g),2),int(sha_256_constants[i],16),int(w_t[i],2)])             t_2=mod_32_addition([int(e_0(a),2),int(Maj(a,b,c),2)])             h=g             g=f             f=e             e=mod_32_addition([int(d,2),t_1])             d=c             c=b             b=a              a=mod_32_addition([t_1,t_2])             a=bin_32bit(a)             e=bin_32bit(e)         if i > 15:             w_t.append(message_schedule(i,w_t))             t_1=mod_32_addition([int(h,2),int(e_1(e),2),int(Ch(e,f,g),2),int(sha_256_constants[i],16),int(w_t[i],2)])             t_2=mod_32_addition([int(e_0(a),2),int(Maj(a,b,c),2)])             h=g             g=f             f=e             e=mod_32_addition([int(d,2),t_1])             d=c             c=b             b=a              a=mod_32_addition([t_1,t_2])             a=bin_32bit(a)             e=bin_32bit(e)     hash_0 = mod_32_addition([dec_return_hex(initial_hash_values[0]),int(a,2)])     hash_1 = mod_32_addition([dec_return_hex(initial_hash_values[1]),int(b,2)])     hash_2 = mod_32_addition([dec_return_hex(initial_hash_values[2]),int(c,2)])     hash_3 = mod_32_addition([dec_return_hex(initial_hash_values[3]),int(d,2)])     hash_4 = mod_32_addition([dec_return_hex(initial_hash_values[4]),int(e,2)])     hash_5 = mod_32_addition([dec_return_hex(initial_hash_values[5]),int(f,2)])     hash_6 = mod_32_addition([dec_return_hex(initial_hash_values[6]),int(g,2)])     hash_7 = mod_32_addition([dec_return_hex(initial_hash_values[7]),int(h,2)])     final_hash = (hex_return(hash_0),                   hex_return(hash_1),                   hex_return(hash_2),                   hex_return(hash_3),                   hex_return(hash_4),                   hex_return(hash_5),                   hex_return(hash_6),                   hex_return(hash_7))     return(final_hash)