Readme for modifications to support RFC 6637 - Elliptic Curve Cryptography (ECC) in OpenPGP

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# Elliptic Curve Cryptography support for OpenPGPjs
## Description
This work is to provide an implementation of [RFC 6637](http://www.ietf.org/rfc/rfc6637.txt)
for OpenPGP.js.
## Compatibility with GnuPG
In order to assure compatibility of the provided implementation with RFC 6637,
the keys and messages were tested against GnuPG version v2.1.8, compiled
with a beta version of libgcrypt v1.7.0-beta262.
It was tested that keys, messages, and signatures generated by GnuPG
were imported correctly. Also keys, messages and signatures generated by this
implementation are correctly imported by GnuPG.
```txt
> gpg2 --homedir ../home --version
gpg (GnuPG) 2.1.8
libgcrypt 1.7.0-beta262
Copyright (C) 2015 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Home: ../home
Supported algorithms:
Pubkey: RSA, ELG, DSA, ECDH, ECDSA, EDDSA
Cipher: IDEA, 3DES, CAST5, BLOWFISH, AES, AES192, AES256, TWOFISH,
CAMELLIA128, CAMELLIA192, CAMELLIA256
Hash: SHA1, RIPEMD160, SHA256, SHA384, SHA512, SHA224
Compression: Uncompressed, ZIP, ZLIB
```
## Extra dependencies
There are two new dependencies:
* [Elliptic](https://github.com/indutny/elliptic/) for the elliptic curve
cryptography. MIT license.
* [Aes](https://github.com/cryptocoinjs/aes) required to implement RFC 3394
Key wrap and Key Unwrap functions. BSD License.
## Examples
### Generate new key
```js
var openpgp = require('openpgp');
var options = {
curve: 'secp256k1',
userIds: {name: 'Hamlet', email: 'hamlet@example.net'},
passphrase: 'To be, or not to be: that is the question'
};
openpgp.generateKey(options).then(function(key) {
// success
var privkey = key.privateKeyArmored;
var pubkey = key.publicKeyArmored;
}).catch(function(error) {
// failure
});
```
### Generate keypair from bitcoin key
```js
var openpgp = require('openpgp');
var bs58check = require('bs58check');
var wif = 'KyiAchQgMKuXQu89j6k6UVZQj7brK6cM79JfmDvkNXPVW24L1thi';
var buff = bs58check.decode(wif);
var privateKey = buff.slice(1, -1);
privateKey = openpgp.util.bin2str(privateKey);
var options = {
curve: 'secp256k1',
userIds: {name: 'Hamlet', email: 'hamlet@example.net'},
passphrase: 'To be, or not to be: that is the question',
material: {
key: privateKey,
subkey: privateKey
}
};
openpgp.generateKey(options).then(function(key) {
// success
var privkey = key.privateKeyArmored;
var pubkey = key.publicKeyArmored;
}).catch(function(error) {
// failure
});
```
### Signature, encryption and decryption
The normal operations: signature, encryption and decryption require
no modifications.
```js
var openpgp = require('openpgp');
var keyData = '-----BEGIN PGP PUBLIC KEY BLOCK ... END PGP PUBLIC KEY BLOCK-----';
var key = openpgp.key.readArmored(keyData);
openpgp.encrypt({publicKeys: key.keys, data: 'Hello, World!'}).then(function(msg) {
// success
}).catch(function(error) {
// failure
});
```
## Possible improvements
* The dependency with AES library can be eliminated, a suitable AES decrypt
function is provided. It is only used by the wrap and unwrap functions
in the crypto/rfc3394.js file.
## Note
Although the example uses the same value to generate the main key, and
the subkey, it is a recommended practice to use different keys.
The main key is used for signature and the subkeys are used for encryption.
## Resources
* Elliptic Curve Cryptography (ECC) in OpenPGP [RFC 6637](http://www.ietf.org/rfc/rfc6637.txt)
* OpenPGP Message Format [RFC 4880](http://www.ietf.org/rfc/rfc4880.txt)
* Advanced Encryption Standard (AES) Key Wrap Algorithm [RFC 3394](http://www.ietf.org/rfc/rfc3394.txt)
* A JavaScript component for the Advanced Encryption Standard (AES) [AES](https://github.com/cryptocoinjs/aes)
* Fast elliptic-curve cryptography in a plain javascript implementation [Elliptic](https://github.com/indutny/elliptic/)