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I am using RSA to encrypt/decrypt my session keys in Python. I am using Pycrypto library. After generating the keypair, I want to extract the private key and public key from that generated key and store them in different files. How can I do this? I can see the has Private method which can tell that the generated keypair has private component but not able to find how to extract both the keys from this generated keypair. Any Suggestion would be of great help.
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To decrypt a ciphertext C using an RSA public key we simply compute the plaintext M as: M = Cd mod N. Note that both RSA encryption and RSA decryption involve a modular exponentiation and so we would be well advised to use the Repeated Squares Algorithm if we want to make these processes reasonably efficient.
An RSA user creates and publishes a public key based on two large prime numbers, along with an auxiliary value. The prime numbers are kept secret. Messages can be encrypted by anyone, via the public key, but can only be decoded by someone who knows the prime numbers.
Step 1: Select two large prime numbers, p, and q. Step 2: Multiply these numbers to find n = p x q, where n is called the modulus for encryption and decryption. Step 3: Choose a number e less that n, such that n is relatively prime to (p - 1) x (q -1).
If you want to get the different parts from the key, there is key attribute for that:
>>> from Crypto.PublicKey import RSA
>>> RSAkey = RSA.generate(1024)
>>> getattr(RSAkey.key, 'n')
13773...L
>>> getattr(RSAkey.key, 'p')
11731...L
>>> getattr(RSAkey.key, 'q')
11740...L
Available components are 'n', 'e', 'd', 'p', 'q', 'u'
If you just want to save it in PEM, you should use exportKey() method (available since 2.2)
>>> private = RSA.generate(1024)
>>> public = private.publickey()
>>> private.exportKey()
'-----BEGIN RSA PRIVATE KEY-----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\n7K5ejL522XsHurVrWdqnk6KvjlRXqB4FsMWLE6RBgBNV0A==\n-----END RSA PRIVATE KEY-----'
>>> public.exportKey()
'-----BEGIN PUBLIC KEY-----\nMIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDo1M0P3nryaF8ZITv8vCFVnjUJ\n1mnIsrqXZRTzjin69xepr3czKicG3EYSUqMODQAsvMj0tGMo+ElGOVOkPFLVVBHd\n8izgA/E1RqUzbUDMj4WnhlhAQq7tNaViOXNaZ7krJZHabZKxfYvLAQtm4tr+m5Nt\nXPBaWvjwhd5M9xvktwIDAQAB\n-----END PUBLIC KEY-----'
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