390 http://inventwithpython.com/hacking

Email questions to the author: [email protected]

RSA Key File Format

makeRsaKeys.py

56. print()


57. print('The public key is a %s and a %s digit number.' %
    (len(str(publicKey[0])), len(str(publicKey[1]))))


58. print('Writing public key to file %s_pubkey.txt...' % (name))


59. fo = open('%s_pubkey.txt' % (name), 'w')


60. fo.write('%s,%s,%s' % (keySize, publicKey[0], publicKey[1]))


61. fo.close()

Line 57 prints some information about the public key. It can tell how many digits are in the
integer in publicKey[0] and publicKey[1] by converting those values to strings with the
str() function, and then finding the length of the string with the len() function.

The key file’s contents will be the key size, a comma, the n integer, another comma, and the e (or
d) integer. The file’s contents will look like: ,,

Lines 59 to 61 open a file in write mode, as you can tell from the 'w' string passed to open().

makeRsaKeys.py

63. print()


64. print('The private key is a %s and a %s digit number.' %
    (len(str(publicKey[0])), len(str(publicKey[1]))))


65. print('Writing private key to file %s_privkey.txt...' % (name))


66. fo = open('%s_privkey.txt' % (name), 'w')


67. fo.write('%s,%s,%s' % (keySize, privateKey[0], privateKey[1]))


68. fo.close()

Lines 63 to 68 do the exact same thing as lines 56 and 61, except for writing the private key out to
a file.

makeRsaKeys.py
7 1. # If makeRsaKeys.py is run (instead of imported as a module) call

72. 
    

    the main() function.

    
    


73. if name == 'main':


74. main()

Lines 73 and 74 are at the bottom of the program, and call main() if makeRsaKeys.py is being
run as a program instead of imported as a module by another program.