ursa-purejs
===========

A pure-js drop-in replacement for URSA, using node-rsa behind the scenes.

> Note : Most of this readme is shamelessly stolen from ursa's own repo.

Installing

``shell
npm install ursa-purejs
`

Simple Encrypt / Decrypt Example
--------------------------------

`javascript
// openssl genrsa -out certs/server/my-server.key.pem 2048
// openssl rsa -in certs/server/my-server.key.pem -pubout -out certs/client/my-server.pub

'use strict';

var fs = require('fs')
, ursa = require('ursa-purejs')
, crt
, key
, msg
;

key = ursa.createPrivateKey(fs.readFileSync('./certs/server/my-server.key.pem'));
crt = ursa.createPublicKey(fs.readFileSync('./certs/client/my-server.pub'));

console.log('Encrypt with Public');
msg = crt.encrypt("Everything is going to be 200 OK", 'utf8', 'base64');
console.log('encrypted', msg, '\n');

console.log('Decrypt with Private');
msg = key.decrypt(msg, 'base64', 'utf8');
console.log('decrypted', msg, '\n');

console.log('############################################');
console.log('Reverse Public -> Private, Private -> Public');
console.log('############################################\n');

crt = ursa.createPrivateKey(fs.readFileSync('./certs/server/my-server.key.pem'));
key = ursa.createPublicKey(fs.readFileSync('./certs/client/my-server.pub'));

console.log('Encrypt with Private (called public)');
msg = key.encrypt("Everything is going to be 200 OK", 'utf8', 'base64');
console.log('encrypted', msg, '\n');

console.log('Decrypt with Public (called private)');
msg = crt.decrypt(msg, 'base64', 'utf8');
console.log('decrypted', msg, '\n');
`

Testing
-------

`shell
npm test
`

Or

`shell
node ./test/test.js
`

No dependencies are necessary here

Usage
-----

This library aims to be convenient to use, allowing one to pass in and
get back regular string objects. However, it is also meant to be reasonably
easy to use efficiently, allowing one to pass in and get back Buffer
objects. Using Buffers is always the more efficient option.

All methods that can deal with strings take one or more arguments indicating
the encoding to use when interpreting an argument or generating a result.
These are limited to the usual encoding names that are valid for use with
Buffers: base64 binary hex and utf8. If an encoding is left undefined
and the argument is a string, then the encoding is always assumed to be
utf8. If an argument is a Buffer, then the encoding (if defined at all)
is ignored. An undefined output encoding is always interpreted as a request
for a Buffer result.

The library knows how to read and output PEM format files for both
public and private keys, and it can generate new private keys (aka
keypairs).

The usual public-encryption / private-decryption operations by default
use padding mode RSA_PKCS1_OAEP_PADDING, which is the recommended
mode for all new applications (as of this writing). Note that this mode
builds-in a random element into every encryption operation, making it
unnecessary to waste time or effort adding randomness in at a higher layer.
This default may be overridden to use the older mode RSA_PKCS1_PADDING
if needed.

> The following is not yet implemented in ursa-purejs

The less well-understood private-encryption / public-decryption operations
(used for building signature mechanisms) are always done using padding
mode RSA_PKCS1_PADDING. This doesn't build in any randomness (but that's
not usually a problem for applications that use these operations).

See the doc comments and tests for the excruciating details, but here's
a quick rundown of the available top-level exports and instance methods:

Top-Level Exports
-----------------

$3

Create and return a private key (aka a keypair) read in from the given
PEM-format file. If defined, the given password is used to decrypt
the PEM file.

The encoding, if specified, applies to both other arguments.

See "Public Key Methods" below for more details.

$3

NOT YET IMPLEMENTED
Create and return a private key from the given components.

$3

Convenient shorthand for assert(ursa.isKey(obj)).

$3

Convenient shorthand for assert(ursa.isPrivateKey(obj)).

$3

Convenient shorthand for assert(ursa.isPublicKey(obj)).

$3

Coerce the given key value into a key object (either public or
private), returning it. If given a private key object, this just
returns it as-is. If given a string or Buffer, it tries to parse it as
PEM. Anything else will result in an error.

$3

Coerce the given key value into a private key object, returning it. If
given a private key object, this just returns it as-is. If given a
string or Buffer, it tries to parse it as PEM. Anything else will
result in an error.

$3

Coerce the given key value into a public key object, returning it. If
given a private key object, this just returns it as-is. If given a
string or Buffer, it tries to parse it as PEM. Anything else will
result in an error.

$3

Create and return a public key read in from the given PEM-format file.
See "Public Key Methods" below for more details.

$3

Create and return a signer which can sign a hash generated with the named
algorithm (such as "sha256" or "md5"). See "Signer Methods" below
for more details.

This function is similar to crypto.createSign(), except this function
takes a hash algorithm name (e.g., "sha256") and not a crypto+hash name
combination (e.g., "RSA-SHA256").

$3

Create and return a verifier which can verify a hash generated with the
named algorithm (such as "sha256" or "md5"). See "Verifier Methods" below
for more details.

This function is similar to crypto.createVerify(), except this function
takes a hash algorithm name (e.g., "sha256") and not a crypto+hash name
combination (e.g., "RSA-SHA256").

$3

This returns true if and only if both arguments are key objects of
the same type (public or private) and their contents match.

$3

Create and return a freshly-generated private key (aka a keypair).
The first argument indicates the number of bits in the modulus (1024
or more is generally considered secure). The second argument indicates
the exponent value, which must be odd (65537 is the typical value; 3
and 17 are also common). Both arguments are optional and default to
2048 and 65537 (respectively).

This method will throw if modulusBits is less than 512 (because
it's pretty crazy to want a key with that few bits) or if exponent
is even (because RSA only works for odd exponents).

Using the command-line openssl tool, this operation is
equivalent to:

`shell
openssl genrsa -out key-name.pem
`

for exponent 65537, or for exponent 3 with the additional option
-3. (That tool doesn't support other exponents.)

$3

Return true if the given object is a key object (public or private) that
was created by this module. Return false if not.

$3

Return true if the given object is a private key object that
was created by this module. Return false if not.

$3

Return true if the given object is a public key object that
was created by this module. Return false if not.

Note that, even though all the public key operations work on private
keys, this function only returns true if the given object is a
public key, per se.

$3

This returns true if and only if both arguments are key objects of
some sort (either can be public or private, and they don't have to
be the same) and their public aspects match each other.

$3

NOT YET IMPLEMENTED
This returns publicKey from ssh-rsa public key-string. First argument
must be a string like ssh-rsa AAAAB3Nz.... user@localhost or Buffer of pubKey bits.

$3

NOT YET IMPLEMENTED
Return the SSH-style public key fingerprint of the given SSH-format
public key (which was, perhaps, the result of a call to
toPublicSsh() on a key object).

This is no more and no less than an MD5 hash of the given SSH-format
public key. This function doesn't actually check to see if the given
key is valid (garbage in, garbage out).

Using the command-line ssh-keygen tool, this operation is
equivalent to:

`shell
ssh-keygen -l -f key-name.sshpub
`

This operation is also equivalent to this:

`shell
cat key-name.sshpub | awk '{print $2}' | base64 --decode | md5
`

Public Key Methods
------------------

These are all the methods available on public keys. These methods are
also available on private keys (since private keys have all the
underlying data necessary to perform the public-side operations).

$3

This performs the "public encrypt" operation on the given buffer. The
result is always a byte sequence that is the same size as the key
associated with the instance. (For example, if the key is 2048 bits,
then the result of this operation will be 2048 bits, aka 256 bytes.)

The input buffer is limited to be no larger than the key size
minus 41 bytes.

If no padding mode is specified, the default, and recommended, mode
is ursa.RSA_PKCS1_OAEP_PADDING. The mode
ursa.RSA_PKCS1_PADDING is also supported.

$3

Get the public exponent as an unsigned big-endian byte sequence.

$3

Get the public modulus as an unsigned big-endian byte sequence.

$3

This is a friendly wrapper for verifying signatures. The given buffer
is hashed using the named algorithm, and the result is verified
against the given signature. This returns true if the hash and
signature match and the signature was produced by the appropriate
private key. This returns false if the signature is a valid signature
(structurally) but doesn't match. This throws an exception in other
cases.

The encoding, if specified, applies to both buffer-like arguments. The
algorithm must always be a string.

$3

NOT YET IMPLEMENTED
This performs the "public decrypt" operation on the given buffer. The
result is always a byte sequence that is no more than the size of the
key associated with the instance. (For example, if the key is 2048
bits, then the result of this operation will be no more than 2048
bits, aka 256 bytes.)

This operation is always performed using padding mode
RSA_PKCS1_PADDING.

$3

This converts the public key data into a PEM-format file.

$3

This converts the public key data into an SSH-format file. This is the
file format one finds in SSH's authorized_keys and known_hosts files.
When used in such files, the contents are base64-encoded and prefixed with
the label ssh-rsa. Depending on context, the line a key appears on may
also have a host name prefix (in known_hosts) or comment suffix
(in authorized_keys).

Using the command-line ssh-keygen tool, this operation is equivalent to:

`shell
ssh-keygen -y -f key-name.pem > key-name.sshpub
`

$3

Return the SSH-style public key fingerprint of this key. See
ursa.sshFingerprint(), above, for more details.

$3

NOT YET IMPLEMENTED
This performs an RSA public-verify on the given hash buffer, which
should be the result of performing the hash operation named by
the algorithm (such as "sha256" or "md5") on some data. The
signature buffer is checked to see if it contains a private-signed
statement of the algorithm and hash. The method returns true if
the signature and hash match, or false if the signature and hash
don't match but the signature is at least a valid signature of
some sort. In any other situation, this throws an exception.

The encoding, if specified, applies to both buffer-like arguments. The
algorithm must always be a string.

This method is the underlying one used as part of the implementation
of the higher-level and much friendlier ursa.createVerifier() and
hashAndVerify().

$3

This is an internal method that is used in the implementation of
ursa.isKey() ursa.isPrivateKey() ursa.isPublicKey() and
associated assertion functions. When called externally, it will
always return undefined.


Private Key Methods
-------------------

These are the methods available on private keys, above and beyond
what is available for public keys.

$3

This performs the "private decrypt" operation on the given buffer. The
result is always a byte sequence that is no more than the size of the
key associated with the instance. (For example, if the key is 2048
bits, then the result of this operation will be no more than 2048
bits, aka 256 bytes.)

If no padding mode is specified, the default, and recommended, mode
is ursa.RSA_PKCS1_OAEP_PADDING. The mode
ursa.RSA_PKCS1_PADDING is also supported.

$3

Get the private exponent as an unsigned big-endian byte sequence. The returned
exponent is not encrypted in any way, so this method should be used with caution.

$3

This is a friendly wrapper for producing signatures. The given buffer
is hashed using the named algorithm, and the result is signed using
the private key held by this instance. The return value of this method
is the signature.

$3

NOT YET IMPLEMENTED
This performs the "private encrypt" operation on the given buffer. The
result is always a byte sequence that is the same size as the key
associated with the instance. (For example, if the key is 2048 bits,
then the result of this operation will be 2048 bits, aka 256 bytes.)

The input buffer is limited to be no larger than the key size
minus 12 bytes.

This operation is always performed using padding mode
RSA_PKCS1_PADDING.

$3

NOT YET IMPLEMENTED
This performs an RSA private-sign on the given hash buffer, which
should be the result of performing the hash operation named by
the algorithm (such as "sha256" or "md5") on some data. The
result of this operation may later be passed to verify() on the
corresponding public key.

This method is the underlying one used as part of the implementation
of the higher-level and much friendlier ursa.createSigner() and
hashAndSign().

$3

This converts the private key data into a PEM-format file. The result
is not encrypted, so it behooves the user of this method to take care
with the result if the key is sensitive from a security standpoint,
which is often the case with such things. (YMMV of course.)


Signer Methods
--------------

These are the methods available on signer objects, which are returned
by ursa.createSigner(). These are similar to the objects returned
from crypto.createSign().

$3

NOT YET IMPLEMENTED
Update the hash in-progress with the given data.

$3

NOT YET IMPLEMENTED
Get the final hash of the data, and sign it using the private key. The
return value is the signature, suitable for later verification.


Verifier Methods
----------------

These are the methods available on verifier objects, which are returned
by ursa.createVerifier(). These are similar to the objects returned
from crypto.createVerify().

$3

NOT YET IMPLEMENTED
Update the hash in-progress with the given data.

$3

NOT YET IMPLEMENTED
Get the final hash of the data, and verify that the given signature
both matches it and was produced by the private key corresponding to
the given public key.

This returns true if the signature and hash match appropriately,
or false if the signature appears to be generally valid (e.g.
structurally) yet doesn't match. This throws an exception in all
other cases.


Constants
---------

Allowed padding modes for public encryption and
private decryption:

* ursa.RSA_PKCS1_PADDING
* ursa.RSA_PKCS1_OAEP_PADDING`