A practical introduction to privacy protection GNU on Windows recommends DSA and ElGamal, but I would like to know how good RSA is to use these days, and if so, what is the minimum key size I should use? Can I use SHA-256 for signing (for compatibility with email clients)?
Also, besides e-ignite: Key types , can you point to other sources for this topic?
Today, the minimum RSA / DSA is 1024 bits, so Elleptical Curves are becoming more used as they are faster and use shorter keys.
To have the same security as AES256, you need a key of at least 3072 bits (384 bytes) ...
Certificate-based email clients are currently a separate item (X.509), but for use with RSA / DSA, the most common option is SHA-1 (which is somewhat weak now).
I recommend to study:
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