Merge pull request TheAlgorithms#318 from psyas/master

Create new cipher - Elgamal cipher key generator

Author: harshildarji

ciphers/elgamal_key_generator.py

@@ -0,0 +1,63 @@
+import os
+import random
+import sys
+import rabin_miller as rabinMiller, cryptomath_module as cryptoMath
+
+min_primitive_root = 3
+
+
+def main():
+    print('Making key files...')
+    makeKeyFiles('elgamal', 2048)
+    print('Key files generation successful')
+
+
+# I have written my code naively same as definition of primitive root
+# however every time I run this program, memory exceeded...
+# so I used 4.80 Algorithm in Handbook of Applied Cryptography(CRC Press, ISBN : 0-8493-8523-7, October 1996)
+# and it seems to run nicely!
+def primitiveRoot(p_val):
+    print("Generating primitive root of p")
+    while True:
+        g = random.randrange(3,p_val)
+        if pow(g, 2, p_val) == 1:
+            continue
+        if pow(g, p_val, p_val) == 1:
+            continue
+        return g
+
+
+def generateKey(keySize):
+    print('Generating prime p...')
+    p = rabinMiller.generateLargePrime(keySize)  # select large prime number.
+    e_1 = primitiveRoot(p)  # one primitive root on modulo p.
+    d = random.randrange(3, p)  # private_key -> have to be greater than 2 for safety.
+    e_2 = cryptoMath.findModInverse(pow(e_1, d, p), p)
+
+    publicKey = (keySize, e_1, e_2, p)
+    privateKey = (keySize, d)
+
+    return publicKey, privateKey
+
+
+def makeKeyFiles(name, keySize):
+    if os.path.exists('%s_pubkey.txt' % name) or os.path.exists('%s_privkey.txt' % name):
+        print('\nWARNING:')
+        print('"%s_pubkey.txt" or "%s_privkey.txt" already exists. \n'
+              'Use a different name or delete these files and re-run this program.' %
+              (name, name))
+        sys.exit()
+
+    publicKey, privateKey = generateKey(keySize)
+    print('\nWriting public key to file %s_pubkey.txt...' % name)
+    with open('%s_pubkey.txt' % name, 'w') as fo:
+        fo.write('%d,%d,%d,%d' % (publicKey[0], publicKey[1], publicKey[2], publicKey[3]))
+
+    print('Writing private key to file %s_privkey.txt...' % name)
+    with open('%s_privkey.txt' % name, 'w') as fo:
+        fo.write('%d,%d' % (privateKey[0], privateKey[1]))
+
+
+if __name__ == '__main__':
+    main()
+