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1.1.1 • Public • Published


Sponsored by Root, built for ACME.js and Greenlock.js

A focused, zero-dependency library that can do exactly one thing really, really well:

  • Generate a Certificate Signing Requests (CSR), and sign it!


  • Universal ECDSA and CSR support that Just Works™
    • NIST P-256 (also known as prime256v1 or secp256r1)
    • PEM, DER, ASN.1, PKCS8 (Private Key), PKIX/SPKI (Public Key)
    • Common Name (CN) Subject
    • Subject Alternative Names (SANs / altnames)
  • Zero Dependencies
    • (no ASN1.js, PKI.js, forge, jrsasign - not even elliptic.js!)
  • Quality
    • Focused
    • Lightweight
    • Well-Commented, Well-Documented
    • Secure
  • Vanilla Node.js
    • no school like the old school
    • easy to read and understand


Given an array of domains it uses the first for the Common Name (CN), also known as Subject, and all of them as the Subject Alternative Names (SANs or altnames).

'use strict';
var edsacsr = require('ecdsa-csr');
var domains = [ '', '', '' ];
return ecdsacsr({ key: key, domains: domains }).then(function (csr) {
  console.log('CSR PEM:');


  • key must be a PEM or DER
    • PEM may be a plain string or a Buffer*
    • DER must be a Buffer*
  • domains must be a list of strings representing domain names
    • correctly handles utf-8
    • you may also use punycoded, if needed
  • subject will be domains[0] by default
    • you shouldn't use this unless you need to
    • you may need to if you need utf-8 for domains, but punycode for the subject

* "Buffer" can be a node Buffer, a JavaScript Uint8Array, or a JavaScript Array which contains only numbers between 0 and 255.

Other useful options:

  • der: true output a der instead of a PEM
  • format: string|Array|Buffer|Uint8Array output the PEM or DER in the desired format.


You can double check that the CSR you get out is actually valid:

# Generate a key 
openssl ecparam -genkey -name prime256v1 -noout -out ./privkey-ec-p256.pem
# Create a CSR 
npx ecdsa-csr ./privkey-ec-p256.pem, > csr.pem
# Verify 
openssl req -text -noout -verify -in csr.pem

Known Issues

I've learned to be careful about talking about the future, however, I literally just published this last night (2018-11-17) and there are a few things I plan to address but haven't yet:

  • JWK not yet supported

New to Crypto?

Just a heads up in case you have no idea what you're doing:

First of all, don't panic.


  • EC stands for Elliptic Curve.
  • DSA stands for Digital Signing Algorithm.
  • EC, ECDSA, and ECDH all belong to the same suite of tools.
  • Private keys are actually keypairs (they contain the public key)
  • NIST P-256, prime256v1, and secp256r1 are all aliases of the same thing

In many cases the terms get used (and misused) interchangably, which can be confusing. You'll survive, I promise.

  • PEM is just a Base64-encoded DER (think JSON as hex or base64)
  • DER is an binary object notation for ASN.1 (think actual stringified JSON or XML)
  • ASN.1 is object notation standard (think JSON, the standard)
  • X.509 is a suite of schemas (think XLST or
  • PKCS#8, PKIK, SPKI are all X.509 schemas (think defining firstName vs first_name vs firstname)

Now forget about all that and just know this:

This library solves your problem if you need EC something-or-other and CSR something-or-other in order to deal with SSL certificates in an internal organization.

If that's not what you're doing, you may want HTTPS and SSL through Greenlock.js, or you may be looking for something else entirely.

Goals vs Non-Goals

This was built for use by ACME.js and Greenlock.js.

Rather than trying to make a generic implementation that works with everything under the sun, this library is intentionally focused on around the use case of generating certificates for ACME services (such as Let's Encrypt).

The primary goal of this project is for this code to do exactly (and all of) what it needs to do - No more, no less.

  • ECDSA support EC (named curve P-256), also known as:
    • NIST P-256
    • prime256v1
    • secp256r1
  • PEM, DER, and JWK
    • Support both ASN.1 private key formats (one supported now)
    • Support both ASN.1 public key formats (one supported now)
  • Vanilla node.js (ECMAScript 5.1)
    • No babel
    • No dependencies

However, there are a few areas where I'd be willing to stretch:

  • Support other universally accepted EC standards
    • (the 384 variety is the only one that comes to mind)
  • Support other PEM formats
    • (the EC-only format comes to mind)
  • Type definition files for altscript languages

It is not a goal of this project to support any EC profiles except those that are universally supported by browsers and are sufficiently secure (overkill is overkill).

A little copying is better than a little dependency. - Go Proverbs by Rob Pike

This code is considered small and focused enough that, rather than making it a dependency in other small projects, I personally just copy over the code.

Hence, all of these projects are MPL-2.0 licensed.



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