[discreditable]

Why would they not use asymmetric encryption?

[rakoo]

Because the paragraph on key generation and management would be 3 times as long as the entire article in its current form ?

Asymmetric encryption solves the problem of transmitting the password safely ("solve" is a rather optimistic word, maybe "delegates" is more appropriate); if you can safely transfer passwords from point to point, then using symmetric encryption is far easier.

[throwawayish]

Asymmetric cryptography transforms key distribution problems into key management problems.

Which is just a different problem, not necessarily an easier one, like you say.

[rakoo]

> Asymmetric cryptography transforms key distribution problems into key management problems.

That's a very nice way to put it, I'm going to reuse that !

[ausjke]

more importantly, they're more cpu intensive and slow to deal with large files

[throwawayish]

Asymmetric encryption adds constant overhead, independent of message size.

Unless you're doing it wrong.

[ausjke]

while not an expert I disagree, encrypt a 1GB file must be different from 1MB file, no matter it is sym or asym encryption. normally Asym is for keys while symmetric encryption is for the real content.

[gcp]

...and why encrypt stuff transferred with scp?

[45h34jh53k4j]

because encryption in transit != encryption at rest. Maybe you don't trust the server you are scp'ing the data to, with encryption at rest you dont' need to.

[gcp]

That's not what the documentation is about, though:

====

Use GPG with the cipher AES256, without the --armour option, and with compression to encrypt your files during inter-host transfers. GPG

Encryption helps protect your files during inter-host file transfers (for example, when using the scp, bbftp, or ftp commands). We recommend GPG (Gnu Privacy Guard), an Open Source OpenPGP-compatible encryption system.

===

scp shouldn't be in that list.

[falcolas]

If your goal is to transfer securely from person to person, 'scp' generally means there's a common server you're accessing - not that you're 'scp'ing directly to the other user's machine. Keeping it secure when "at rest" on the remote server would ensure it's securely transferred between the two end points.

[jph]

NASA has historically done at least some open transfers, such as HTTP, FTP, etc. Using GPG for these is good. And it keeps the file encrypted at rest too.

[jph]

Symmetric is easier to teach to people, especially large groups of people doing tech training.

[brockers]

GPG, of course, allows you to use asymmetric crypto and currently supports RSA, RSA-E, RSA-S, ELG-E, and DSA algorithms for that purpose.

But for bulk data encrypting good symmetric (AES, CAST5, etc.) is both more secure and significantly faster.

[raimue]

You should be aware that even for asymmetric encryption, only a one-time document-specific key will be encrypted with the asymmetric algorithm. The document itself will always be encrypted using a symmetric cipher.

This is how the same document can be encrypted for multiple recipients efficiently, without duplication all the data. First the document is encrypted with a symmetric key, which is then encrypted with the public key of each recipient. This information will be prepended to the actual encrypted document.

For details see: https://tools.ietf.org/html/rfc4880#section-2.1

[Xophmeister]

GPG 2.1 (via libgcrypt) also supports various elliptic curve algorithms for asymmetric crypto, depending on what version of libgcrypt you have.