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0 pointsisilofi2y ago0 comments

I'm using RSA8192 with SSH and not seeing any noticable performance problems. ECC is generally faster than RSA, so just always using Ed448 or even larger should be a no-brainer.

0 comments

throw0101a2y ago

Your personal RSA/ECC SSH keys are there for the initial key exchange, after which a session key is created (cycled after x bytes / y seconds).

But if you're handling hundreds or thousands of operations per second (e.g., a web site), then the delays add up.

isilofiOP2y ago

If you are doing hundreds or thousands of SSH connections per second, you are doing something wrong. At least in 99.9% of cases.

Github might be different, but not the rest of the world.

throw0101a2y ago

The comments about Ed25519 versus Ed448 were meant for the general case of their use, and not (necessarily) strictly in the use for SSH.

However, the reason for Ed25519 use in OpenSSH is because the keys are much smaller, and easier to cut/paste/etc, for the same security factor. The fact that they are faster for signing is a bonus.

* https://lists.mindrot.org/pipermail/openssh-unix-dev/2023-Se...

RFC 8032 § 7.1. Test Vectors for Ed25519:

    SECRET KEY:
    9d61b19deffd5a60ba844af492ec2cc44449c5697b326919703bac031cae7f60
    
    PUBLIC KEY:
    d75a980182b10ab7d54bfed3c964073a0ee172f3daa62325af021a68f707511a

RFC 8032 § 7.4. Test Vectors for Ed448

    SECRET KEY:
    6c82a562cb808d10d632be89c8513ebf6c929f34ddfa8c9f63c9960ef6e348a3
    528c8a3fcc2f044e39a3fc5b94492f8f032e7549a20098f95b

    PUBLIC KEY:
    5fd7449b59b461fd2ce787ec616ad46a1da1342485a70e1f8a0ea75d80e96778
    edf124769b46c7061bd6783df1e50f6cd1fa1abeafe8256180

A comparable RSA 3072 key is much longer:

* https://www.scottbrady91.com/openssl/creating-rsa-keys-using...

* https://goteleport.com/blog/comparing-ssh-keys/

All of the above correspond to roughly the security of AES 128. If you want AES 256 equivalence, double the size/length.

I'm in the habit of using ssh-copy-id(1), but there are a lot of places where you have to copy-paste in a web interface (and lots of instructions tell you to copy-paste into your remote ~/.ssh/authorized_keys file).

tiffanyh2y ago

Is it a coincidence the generated keys start with the same first 3 letters (“MII…”)?

1 more reply

isilofiOP2y ago

Length is then not an argument against always using Ed448 over Ed25519.

j / k navigate · click thread line to collapse

0 comments

throw0101a2y ago

Your personal RSA/ECC SSH keys are there for the initial key exchange, after which a session key is created (cycled after x bytes / y seconds).

But if you're handling hundreds or thousands of operations per second (e.g., a web site), then the delays add up.

isilofiOP2y ago

If you are doing hundreds or thousands of SSH connections per second, you are doing something wrong. At least in 99.9% of cases.

Github might be different, but not the rest of the world.

throw0101a2y ago

The comments about Ed25519 versus Ed448 were meant for the general case of their use, and not (necessarily) strictly in the use for SSH.

However, the reason for Ed25519 use in OpenSSH is because the keys are much smaller, and easier to cut/paste/etc, for the same security factor. The fact that they are faster for signing is a bonus.

* https://lists.mindrot.org/pipermail/openssh-unix-dev/2023-Se...

RFC 8032 § 7.1. Test Vectors for Ed25519:

    SECRET KEY:
    9d61b19deffd5a60ba844af492ec2cc44449c5697b326919703bac031cae7f60
    
    PUBLIC KEY:
    d75a980182b10ab7d54bfed3c964073a0ee172f3daa62325af021a68f707511a

RFC 8032 § 7.4. Test Vectors for Ed448

    SECRET KEY:
    6c82a562cb808d10d632be89c8513ebf6c929f34ddfa8c9f63c9960ef6e348a3
    528c8a3fcc2f044e39a3fc5b94492f8f032e7549a20098f95b

    PUBLIC KEY:
    5fd7449b59b461fd2ce787ec616ad46a1da1342485a70e1f8a0ea75d80e96778
    edf124769b46c7061bd6783df1e50f6cd1fa1abeafe8256180

A comparable RSA 3072 key is much longer:

* https://www.scottbrady91.com/openssl/creating-rsa-keys-using...

* https://goteleport.com/blog/comparing-ssh-keys/

All of the above correspond to roughly the security of AES 128. If you want AES 256 equivalence, double the size/length.

tiffanyh2y ago

Is it a coincidence the generated keys start with the same first 3 letters (“MII…”)?

1 more reply

isilofiOP2y ago

Length is then not an argument against always using Ed448 over Ed25519.

j / k navigate · click thread line to collapse