我可以在Java中实现端到端加密吗？

Question

I'm creating a web service that stores a list of users with their public keys online, as well as encrypted messages. My end goal was end-to-end encryption.

I initially thought this would be pretty easy -- "Oh, OpenSSL and RSA private/public key asymmetric encryption is great." False. RSA will only encrypt a tiny bit of data, presumably to pass a regular, symmetric key back and forth.

Okay, so I tried to find solutions online. Most of them either ended without a functioning example or pointed at using the command line , all of which seemed excessive and incomplete.

Is there a way to use end-to-end encryption on data with asymmetric keys, or is it all a personal pipe dream? OpenSSL in PHP has a way to do this already , and it's kludgy but it works.

Is there some method I'm missing here?

Answer 1

The common way to encrypt larger amount of data with a asymmetric keys (eg. RSA ) is by use of hybrid encryption . In hybrid encryption you mix symmetric and asymmetric encryption . First you generated a random symmetric key, that is used to encrypt the data. Then you encrypt the symmetric key with the asymmetric key. The encrypted data + the encrypted random key are then put together and makes up the full encrypted data.

The openssl_seal() in PHP you refer to, uses hybrid encryption where the symmetric algorithm is RC4. How data is encoded and put together in the encrypted files have been defined by the openssl implementation, and might not necessarily be the way you would want to do it. PGP, as an other example of hybrid encryption, uses it's own way of packing the data.

In any case, hybrid encryption is not something you get out of the box in java, and you typically need to implement each of the encryption + packaging steps yourself, or use one of the libraries that implements there version of this. An example of doing it yourself is this Java code I found that can decrypt messages encrypted with the above mentioned openssl_seal() .

An example of using a library for hybrid encryption, could be using the PGP support in Bouncy Castle .

Answer 2

I'm not really sure what you're trying to en- and decrypt, but GnuPG for Java might be a good choice.

It supports public and private keys and can en- and decrypt bigger files and data.

Answer 3

Ebbe's answer is very good, however this question was highly ranked in Google in my attempt to try and find a decent hybrid encryption library (Bouncy Castle's documentation is non-existent and not straight-forward, and GnuPG for Java relies on the OS and is not fully tested). So I thought I'd add on to Ebbe's answer for the weary traveller.

If you can use them, JWTs (JavaScript Web Tokens) could be handy for this. It's also an IETF Standard . There are two different types:

• JWS, which is a signed JWT. Plain-text message, but you can verify its authenticity. Which has its own IETF Standard

• JWE, which is an encrypted JWT. Which also has its own IETF Standard

Support for JWEs are unfortunately a bit poor at this point in time. However this should hopefully improve. At this point in time (2017-04-11), the only Java JWT library that supports JWEs is BitBucket's Jose4j .