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How small can a detached PGP signature be? The only size I get is 287 bytes for a 2048-bit key and 543 bytes for a 4096-bit key, regardless of the size of the data being signed. However, on this post from 2004, the author says he can get a 65-byte detached signature. How is that possible, and is there still a way to do it?

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  • You can't get smaller than the key size using RSA. Some additional overhead for metadata and headers will be added, I recently provided a similar discussion in How to use GnuPG to get the smallest possible output (symmetric encryption)? which mostly also applies to signatures.
    – Jens Erat
    Oct 31, 2017 at 17:24
  • Can El Gamal encrypt something to be smaller than the key size? Nov 1, 2017 at 2:35
  • I got a digital signature down to 96 bytes. But when I'm encrypting, is it not possible to shrink the output without using symmetric encryption? Nov 1, 2017 at 14:04
  • What do you mean? OpenPGP is a hybrid cryptosystem, which always encrypts data with symmetric encryption and only uses public/private key cryptography to encrypt the symmetric session key.
    – Jens Erat
    Nov 1, 2017 at 15:19
  • So you're saying that the reason PGP encryption of 1 byte is big (>500 bytes) is because it has to embed a public key? Nov 1, 2017 at 19:03

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