RSA-SHA512 in Apex

This solution stands of the shoulders of a number of people who provided reference
implementations and ideas. We wish to express appreciation for their published work:

• RSA key utility by Kenju Urushima https://github.com/kjur/jsrsasign
• ASN.1 parser by Lapo Luchini https://github.com/lapo-luchini/asn1js
• BIGINT math by Tom Hu http://www-cs-students.stanford.edu/~tjw
• SHA512 message digest by Michael Tritton https://github.com/trittimo/SHA512

1. A private key file holds secret prime numbers
2. An ASN key reader handles the binary file format
3. The message to sign consists of a JSON Web Token
4. Then a SHA512 hash reduces the message to a big integer
5. Finally the RSA signer executes the modPow signature math

Usage:

Blob signature = CryptoRsaSha512.sign(message, privateKey);

While we can't provide ad-hoc support for this code, please contact us with your company
name and address if you need a warranty for its use and we will assist: www.streamscript.com/contact