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I am confused. When I see HN or facebook certs they show 128 bit encryption in the browser box. 128 bit seems pretty low.

by Achshar 13y ago

mpyne 13y ago
128 talks about symmetric key encryption, not RSA. I'm not sure what the crypto best practice is regarding key strength for 128 bit for symmetric crypto, but presumably it would depend on the cipher used.
F30 13y ago
This is the size of the AES key. AES is a symmetric algorithm and 128 bit are still considered solid there, although the trend is moving towards 256 bit. What we're talking about here is the key size of RSA, which is an asymmetric algorithm. If you don't know the difference, go find a basic crypto tutorial. As you can read above, 1024 bit RSA is probably borken. I wouldn't trust 2048 bit too much as well. Also, progress in breaking RSA is happening a lot faster than with AES. In the context of SSL, an assymetric algorithm like RSA is used to exchange symmetrc keys, which are used afterwards.
- XorNot 13y ago
  That said, 256-bit isn't really that much of an improvement for AES - its favored since that's the US standard for Top Secret classification, but in practice any attack which brings down AES-128 will almost certainly get AES-256 as well. I've switched most of my SSH servers over to default to 128-bit AES ciphers since the difference in difficulty seems small enough that it won't matter if someone actually tries targeting it and can succeed.
mcovey 13y ago
Probably AES, not RSA. IIRC a 128-bit AES key is about equivalent in security to a 2048-bit RSA key.
- caf 13y ago
  2048 bit RSA is usually described as roughly equivalent in security margin to a 112 bit symmetric key, and 3072 bit RSA to be 128 bit symmetric equivalent.
korethr 13y ago
In that case, you are seeing the size of the symmetric key being used. The bigger numbers mentioned above (1024, 2048, etc) are referring to the size of the public/asymmetric keys. The public keys are only used to set up the initial exchange of symmetric keys, which are then used to secure your browser's encrypted connection.

I am confused. When I see HN or facebook certs they show 128 bit encryption in the browser box. 128 bit seems pretty low.

by Achshar 13y ago

I am confused. When I see HN or facebook certs they show 128 bit encryption in the browser box. 128 bit seems pretty low.

mpyne 13y ago

128 talks about symmetric key encryption, not RSA. I'm not sure what the crypto best practice is regarding key strength for 128 bit for symmetric crypto, but presumably it would depend on the cipher used.

F30 13y ago

This is the size of the AES key. AES is a symmetric algorithm and 128 bit are still considered solid there, although the trend is moving towards 256 bit. What we're talking about here is the key size of RSA, which is an asymmetric algorithm. If you don't know the difference, go find a basic crypto tutorial. As you can read above, 1024 bit RSA is probably borken. I wouldn't trust 2048 bit too much as well. Also, progress in breaking RSA is happening a lot faster than with AES. In the context of SSL, an assymetric algorithm like RSA is used to exchange symmetrc keys, which are used afterwards.

XorNot 13y ago
That said, 256-bit isn't really that much of an improvement for AES - its favored since that's the US standard for Top Secret classification, but in practice any attack which brings down AES-128 will almost certainly get AES-256 as well. I've switched most of my SSH servers over to default to 128-bit AES ciphers since the difference in difficulty seems small enough that it won't matter if someone actually tries targeting it and can succeed.

mcovey 13y ago

Probably AES, not RSA. IIRC a 128-bit AES key is about equivalent in security to a 2048-bit RSA key.

caf 13y ago
2048 bit RSA is usually described as roughly equivalent in security margin to a 112 bit symmetric key, and 3072 bit RSA to be 128 bit symmetric equivalent.

korethr 13y ago

In that case, you are seeing the size of the symmetric key being used. The bigger numbers mentioned above (1024, 2048, etc) are referring to the size of the public/asymmetric keys. The public keys are only used to set up the initial exchange of symmetric keys, which are then used to secure your browser's encrypted connection.