diff --git a/bin/rsa-csr.js b/bin/rsa-csr.js
index e9cbdcb..a923330 100755
--- a/bin/rsa-csr.js
+++ b/bin/rsa-csr.js
@@ -7,9 +7,15 @@ var rsacsr = require('../index.js');
 var keyname = process.argv[2];
 var domains = process.argv[3].split(/,/);
 
-var keypem = fs.readFileSync(keyname, 'ascii');
+var key = fs.readFileSync(keyname, 'ascii');
 
-rsacsr({ key: keypem, domains: domains }).then(function (csr) {
+try {
+  key = JSON.parse(key);
+} catch(e) {
+  // ignore
+}
+
+rsacsr({ key: key, domains: domains }).then(function (csr) {
   // Using error so that we can redirect stdout to file
   //console.error("CN=" + domains[0]);
   //console.error("subjectAltName=" + domains.join(','));
diff --git a/fixtures/whatever.net-www-api.csr.pem b/fixtures/whatever.net-www-api.csr.pem
new file mode 100644
index 0000000..9275f2d
--- /dev/null
+++ b/fixtures/whatever.net-www-api.csr.pem
@@ -0,0 +1,17 @@
+-----BEGIN CERTIFICATE REQUEST-----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+-----END CERTIFICATE REQUEST-----
diff --git a/index.js b/index.js
index d2e8011..a4b74e6 100644
--- a/index.js
+++ b/index.js
@@ -1,2 +1,2 @@
 'use strict';
-module.exports = require('./lib/rsa-csr.js');
+module.exports = require('./lib/csr.js');
diff --git a/lib/asn1.js b/lib/asn1.js
index e69de29..c92c1c3 100644
--- a/lib/asn1.js
+++ b/lib/asn1.js
@@ -0,0 +1,72 @@
+'use strict';
+
+//
+// A dumbed-down, minimal ASN.1 parser / packer combo
+//
+// Note: generally I like to write congruent code
+// (i.e. output can be used as input and vice-versa)
+// However, this seemed to be more readable and easier
+// to use written as-is, asymmetrically.
+// (I also generally prefer to export objects rather
+// functions but, yet again, asthetics one in this case)
+
+var Enc = require('./encoding.js');
+
+//
+// Packer
+//
+
+// Almost every ASN.1 type that's important for CSR
+// can be represented generically with only a few rules.
+var ASN1 = module.exports = function ASN1(/*type, hexstrings...*/) {
+  var args = Array.prototype.slice.call(arguments);
+  var typ = args.shift();
+  var str = args.join('').replace(/\s+/g, '').toLowerCase();
+  var len = (str.length/2);
+  var lenlen = 0;
+  var hex = typ;
+
+  // We can't have an odd number of hex chars
+  if (len !== Math.round(len)) {
+    console.error(arguments);
+    throw new Error("invalid hex");
+  }
+
+  // The first byte of any ASN.1 sequence is the type (Sequence, Integer, etc)
+  // The second byte is either the size of the value, or the size of its size
+
+  // 1. If the second byte is < 0x80 (128) it is considered the size
+  // 2. If it is > 0x80 then it describes the number of bytes of the size
+  //    ex: 0x82 means the next 2 bytes describe the size of the value
+  // 3. The special case of exactly 0x80 is "indefinite" length (to end-of-file)
+
+  if (len > 127) {
+    lenlen += 1;
+    while (len > 255) {
+      lenlen += 1;
+      len = len >> 8;
+    }
+  }
+
+  if (lenlen) { hex += Enc.numToHex(0x80 + lenlen); }
+  return hex + Enc.numToHex(str.length/2) + str;
+};
+
+// The Integer type has some special rules
+ASN1.UInt = function UINT() {
+  var str = Array.prototype.slice.call(arguments).join('');
+  var first = parseInt(str.slice(0, 2), 16);
+
+  // If the first byte is 0x80 or greater, the number is considered negative
+  // Therefore we add a '00' prefix if the 0x80 bit is set
+  if (0x80 & first) { str = '00' + str; }
+
+  return ASN1('02', str);
+};
+
+// The Bit String type also has a special rule
+ASN1.BitStr = function BITSTR() {
+  var str = Array.prototype.slice.call(arguments).join('');
+  // '00' is a mask of how many bits of the next byte to ignore
+  return ASN1('03', '00' + str);
+};
diff --git a/lib/csr.js b/lib/csr.js
new file mode 100644
index 0000000..73654c6
--- /dev/null
+++ b/lib/csr.js
@@ -0,0 +1,122 @@
+'use strict';
+
+var crypto = require('crypto');
+var ASN1 = require('./asn1.js');
+var Enc = require('./encoding.js');
+var PEM = require('./pem.js');
+var X509 = require('./x509.js');
+var RSA = {};
+
+/*global Promise*/
+var CSR = module.exports = function rsacsr(opts) {
+  // We're using a Promise here to be compatible with the browser version
+  // which will probably use the webcrypto API for some of the conversions
+  return Promise.resolve().then(function () {
+    var Rasha;
+    opts = JSON.parse(JSON.stringify(opts));
+    var pem, jwk;
+
+    // We do a bit of extra error checking for user convenience
+    if (!opts) { throw new Error("You must pass options with key and domains to rsacsr"); }
+    if (!Array.isArray(opts.domains) || 0 === opts.domains.length) {
+      new Error("You must pass options.domains as a non-empty array");
+    }
+
+    // I need to check that 例.中国 is a valid domain name
+    if (!opts.domains.every(function (d) {
+      // allow punycode? xn--
+      if ('string' === typeof d /*&& /\./.test(d) && !/--/.test(d)*/) {
+        return true;
+      }
+    })) {
+      throw new Error("You must pass options.domains as strings");
+    }
+
+    if (opts.pem) {
+      pem = opts.pem;
+    } else if (opts.jwk) {
+      jwk = opts.jwk;
+    } else {
+      if (!opts.key) {
+        throw new Error("You must pass options.key as a JSON web key");
+      } else if (opts.key.kty) {
+        jwk = opts.key;
+      } else {
+        pem = opts.key;
+      }
+    }
+
+    if (pem) {
+      try {
+        Rasha = require('rasha');
+      } catch(e) {
+        throw new Error("Rasha.js is an optional dependency for PEM-to-JWK.\n"
+          + "Install it if you'd like to use it:\n"
+          + "\tnpm install --save rasha\n"
+          + "Otherwise supply a jwk as the private key."
+        );
+      }
+      jwk = Rasha.importSync({ pem: pem });
+    }
+
+    opts.jwk = jwk;
+    return CSR.create(opts).then(function (bytes) {
+      return PEM.packBlock({
+        type: "CERTIFICATE REQUEST"
+      , bytes: bytes /* { jwk: jwk, domains: opts.domains } */
+      });
+    });
+  });
+};
+
+CSR.create = function createCsr(opts) {
+  var hex = CSR.request(opts.jwk, opts.domains);
+  return CSR.sign(opts.jwk, hex).then(function (csr) {
+    return Enc.hexToBuf(csr);
+  });
+};
+
+CSR.request = function createCsrBodyEc(jwk, domains) {
+  var asn1pub = X509.packCsrPublicKey(jwk);
+  return X509.packCsr(asn1pub, domains);
+};
+
+CSR.sign = function csrEcSig(jwk, request) {
+  var keypem = PEM.packBlock({ type: "RSA PRIVATE KEY", bytes: X509.packPkcs1(jwk) });
+
+  return RSA.sign(keypem, Enc.hexToBuf(request)).then(function (sig) {
+    var sty = ASN1('30'
+      // 1.2.840.113549.1.1.11 sha256WithRSAEncryption (PKCS #1)
+    , ASN1('06', '2a864886f70d01010b')
+    , ASN1('05')
+    );
+    return ASN1('30'
+      // The Full CSR Request Body
+    , request
+      // The Signature Type
+    , sty
+      // The Signature
+    , ASN1.BitStr(Enc.bufToHex(sig))
+    );
+  });
+};
+
+//
+// RSA
+//
+
+// Took some tips from https://gist.github.com/codermapuche/da4f96cdb6d5ff53b7ebc156ec46a10a
+RSA.sign = function signRsa(keypem, ab) {
+  return Promise.resolve().then(function () {
+    // Signer is a stream
+    var sign = crypto.createSign('SHA256');
+    sign.write(new Uint8Array(ab));
+    sign.end();
+
+    // The signature is ASN1 encoded, as it turns out
+    var sig = sign.sign(keypem);
+
+    // Convert to a JavaScript ArrayBuffer just because
+    return new Uint8Array(sig.buffer.slice(sig.byteOffset, sig.byteOffset + sig.byteLength));
+  });
+};
diff --git a/lib/encoding.js b/lib/encoding.js
index e69de29..f6b6ab0 100644
--- a/lib/encoding.js
+++ b/lib/encoding.js
@@ -0,0 +1,34 @@
+'use strict';
+
+var Enc = module.exports;
+
+Enc.base64ToHex = function base64ToHex(b64) {
+  return Buffer.from(b64, 'base64').toString('hex').toLowerCase();
+};
+
+Enc.bufToBase64 = function bufToBase64(u8) {
+  // we want to maintain api compatability with browser APIs,
+  // so we assume that this could be a Uint8Array
+  return Buffer.from(u8).toString('base64');
+};
+
+Enc.bufToHex = function toHex(u8) {
+  return Buffer.from(u8).toString('hex').toLowerCase();
+};
+
+Enc.hexToBuf = function (hex) {
+  return Buffer.from(hex, 'hex');
+};
+
+Enc.numToHex = function numToHex(d) {
+  d = d.toString(16);
+  if (d.length % 2) {
+    return '0' + d;
+  }
+  return d;
+};
+
+Enc.utf8ToHex = function utf8ToHex(str) {
+  // node can properly handle utf-8 strings
+  return Buffer.from(str).toString('hex').toLowerCase();
+};
diff --git a/lib/pem.js b/lib/pem.js
index e69de29..1c0f709 100644
--- a/lib/pem.js
+++ b/lib/pem.js
@@ -0,0 +1,12 @@
+'use strict';
+
+var Enc = require('./encoding.js')
+var PEM = module.exports;
+
+PEM.packBlock = function (opts) {
+  // TODO allow for headers?
+  return '-----BEGIN ' + opts.type + '-----\n'
+    + Enc.bufToBase64(opts.bytes).match(/.{1,64}/g).join('\n') + '\n'
+    + '-----END ' + opts.type + '-----'
+  ;
+};
diff --git a/lib/rsa-csr.js b/lib/rsa-csr.js
deleted file mode 100644
index e83b7ef..0000000
--- a/lib/rsa-csr.js
+++ /dev/null
@@ -1,5 +0,0 @@
-'use strict';
-
-module.exports = function rsacsr(opts) {
-  throw new Error("not implemented yet");
-};
diff --git a/lib/x509.js b/lib/x509.js
index e69de29..33cb9c5 100644
--- a/lib/x509.js
+++ b/lib/x509.js
@@ -0,0 +1,66 @@
+'use strict';
+
+var ASN1 = require('./asn1.js');
+var Enc = require('./encoding.js');
+
+var X509 = module.exports;
+
+X509.packCsr = function (asn1pubkey, domains) {
+  return ASN1('30'
+    // Version (0)
+  , ASN1.UInt('00')
+
+    // 2.5.4.3 commonName (X.520 DN component)
+  , ASN1('30', ASN1('31', ASN1('30', ASN1('06', '550403'), ASN1('0c', Enc.utf8ToHex(domains[0])))))
+
+    // Public Key (RSA or EC)
+  , asn1pubkey
+
+    // Request Body
+  , ASN1('a0'
+    , ASN1('30'
+        // 1.2.840.113549.1.9.14 extensionRequest (PKCS #9 via CRMF)
+      , ASN1('06', '2a864886f70d01090e')
+      , ASN1('31'
+        , ASN1('30'
+          , ASN1('30'
+              // 2.5.29.17 subjectAltName (X.509 extension)
+            , ASN1('06', '551d11')
+            , ASN1('04'
+              , ASN1('30', domains.map(function (d) {
+                  return ASN1('82', Enc.utf8ToHex(d));
+                }).join(''))))))))
+  );
+};
+
+X509.packPkcs1 = function (jwk) {
+  var n = ASN1.UInt(Enc.base64ToHex(jwk.n));
+  var e = ASN1.UInt(Enc.base64ToHex(jwk.e));
+
+  if (!jwk.d) {
+    return Enc.hexToBuf(ASN1('30', n, e));
+  }
+
+  return Enc.hexToBuf(ASN1('30'
+  , ASN1.UInt('00')
+  , n
+  , e
+  , ASN1.UInt(Enc.base64ToHex(jwk.d))
+  , ASN1.UInt(Enc.base64ToHex(jwk.p))
+  , ASN1.UInt(Enc.base64ToHex(jwk.q))
+  , ASN1.UInt(Enc.base64ToHex(jwk.dp))
+  , ASN1.UInt(Enc.base64ToHex(jwk.dq))
+  , ASN1.UInt(Enc.base64ToHex(jwk.qi))
+  ));
+};
+
+X509.packCsrPublicKey = function (jwk) {
+  // Sequence the key
+  var n = ASN1.UInt(Enc.base64ToHex(jwk.n));
+  var e = ASN1.UInt(Enc.base64ToHex(jwk.e));
+  var asn1pub = ASN1('30', n, e);
+  //var asn1pub = X509.packPkcs1({ kty: jwk.kty, n: jwk.n, e: jwk.e });
+
+  // Add the CSR pub key header
+  return ASN1('30', ASN1('30', ASN1('06', '2a864886f70d010101'), ASN1('05')), ASN1.BitStr(asn1pub));
+};
diff --git a/test.sh b/test.sh
index d3fb11e..c53b247 100755
--- a/test.sh
+++ b/test.sh
@@ -1,6 +1,7 @@
 #!/bin/bash
+set -e
 
-gencsr() {
+gencsr2() {
   keyfile=$1
   domain=$2
   csrfile=$3
@@ -22,4 +23,65 @@ DNS.2 = www.$domain") \
     -out $csrfile
 }
 
-gencsr fixtures/privkey-rsa-2048.pkcs1.pem example.com fixtures/example.com-www.csr.pem
+gencsr3() {
+  keyfile=$1
+  domain=$2
+  csrfile=$3
+  openssl req -key $keyfile -new -nodes \
+    -config <(printf "[req]
+prompt = no
+req_extensions = req_ext
+distinguished_name = dn
+
+[ dn ]
+CN = $domain
+
+[ req_ext ]
+subjectAltName = @alt_names
+
+[ alt_names ]
+DNS.1 = $domain
+DNS.2 = www.$domain
+DNS.3 = api.$domain") \
+    -out $csrfile
+}
+
+rndcsr() {
+  keysize=$1
+	openssl genrsa -out fixtures/valid.pkcs1.1.pem $keysize
+  rasha fixtures/valid.pkcs1.1.pem > fixtures/test.jwk.1.json
+  gencsr3 fixtures/valid.pkcs1.1.pem whatever.net fixtures/valid.csr.1.pem
+  node bin/rsa-csr.js fixtures/test.jwk.1.json whatever.net,www.whatever.net,api.whatever.net \
+    > fixtures/test.csr.1.pem
+  diff fixtures/valid.csr.1.pem fixtures/test.csr.1.pem
+}
+
+echo ""
+echo "Generating CSR for example.com,www.example.com"
+gencsr2 fixtures/privkey-rsa-2048.pkcs1.pem example.com fixtures/example.com-www.csr.pem
+node bin/rsa-csr.js fixtures/privkey-rsa-2048.jwk.json example.com,www.example.com \
+  > fixtures/example.com-www.csr.1.pem
+diff fixtures/example.com-www.csr.pem fixtures/example.com-www.csr.1.pem
+echo "Pass"
+
+echo ""
+echo "Generating CSR for whatever.net,www.whatever.net,api.whatever.net"
+gencsr3 fixtures/privkey-rsa-2048.pkcs1.pem whatever.net fixtures/whatever.net-www-api.csr.pem
+node bin/rsa-csr.js fixtures/privkey-rsa-2048.jwk.json whatever.net,www.whatever.net,api.whatever.net \
+  > fixtures/whatever.net-www-api.csr.1.pem
+diff fixtures/whatever.net-www-api.csr.pem fixtures/whatever.net-www-api.csr.1.pem
+echo "Pass"
+
+echo ""
+echo "Generating random keys of various lengths and re-running tests for each"
+rndcsr 3072
+rndcsr 1024
+rndcsr 512 # minimum size that can reasonably work
+echo "Pass"
+
+rm fixtures/*.1.*
+
+echo ""
+echo "All tests passed!"
+echo "  • Fixture CSRs built and do not differ from OpenSSL-generated CSRs"
+echo "  • Random keys and CSRs are also correct"