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I'm using pycrypto to encrypt files that will be stored in the cloud. I expect the user to enter a password to decrypt files, but encryption shouldn't require a password (to allow the script to be run by cron). So therefore I've been looking at public key encryption using RSA under the PKCS1_OAEP cipher.

I can see how to encrypt a file using pycrypto, but is there a pre-existing method to perform authenticated encryption, or am I expected to implement that myself? There's a parameter to pass a hashing algorithm to Crypto.Cipher.PKCS1_OAEP.new(), but will this be used to sign encrypted data?

Similarly to verify before decryption, is this all built into the decrypt() method?

Note: I don't have any particular attachment to pycrypto - if another python crypto library provides an authenticated encryption scheme, please suggest that instead.

Thanks

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PGP (python-gnupg) really sounds like the way you want to go.

Public key crypto is messy because the actual asymmetric cipher is only used to encrypt a one-time session key, which is then used with symmetric crypto (e.g. AES) to encrypt your files. Managing all of that manually would be a headache. But PGP already has all of the details worked out, you just have to call the appropriate functions.

Plus, you have pre-built CLI tools (gpg) to allow you to work with messages outside your app.

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  • Do you know whether pycrypto provides authenticated encryption.
    – Andrew
    Jan 24, 2013 at 17:27
  • Pycrypto provides access to cryptographic primitives and common algorithms. If you want something specific, you have to know specifically what you want. As in, which algorithm.
    – tylerl
    Jan 24, 2013 at 20:13
  • OCB or GCM ideally
    – Andrew
    Jan 25, 2013 at 10:09

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