Generating RSA-SHA1 signatures with JavaScript

Question

I'd like to generate RSA-SHA1 signatures with the RSA-Sign JavaScript Library. Specifically, I'd like to use this for signing OAuth requests.

However, the signature generated by the JavaScript library looks different to the one I can generate e.g. with

$ echo -n "x" | openssl dgst -sha1 -sign priv.key -binary | openssl base64 | xargs echo -n
eV0ZrD7ZrTsuzHHYSwLfUJhXuM96D6ZyIzD5FFphzHbKRaO4TMeTR7bJjkuPib+l
EccM7t6YNDvRgOHyXJDVZZQTg5G4D4jnGVmOgeuti1etCCpLsb1Rl3sfJF/rIlgA
AmejvBbrEG+n8L+GeD6Vd3cneW7k2Rksnh+/BWnnR3c=

In contrast: This is what the library generates (base64 encoded):

Nzk1ZDE5YWMzZWQ5YWQzYjJlY2M3MWQ4NGIwMmRmNTA5ODU3YjhjZjdhMGZhNjcy
MjMzMGY5MTQ1YTYxY2M3Ng0KY2E0NWEzYjg0Y2M3OTM0N2I2Yzk4ZTRiOGY4OWJm
YTUxMWM3MGNlZWRlOTgzNDNiZDE4MGUxZjI1YzkwZDU2NQ0KOTQxMzgzOTFiODBm
ODhlNzE5NTk4ZTgxZWJhZDhiNTdhZDA4MmE0YmIxYmQ1MTk3N2IxZjI0NWZlYjIy
NTgwMA0KMDI2N2EzYmMxNmViMTA2ZmE3ZjBiZjg2NzgzZTk1Nzc3NzI3Nzk2ZWU0
ZDkxOTJjOWUxZmJmMDU2OWU3NDc3Nw==

(assuming the same input & key, of course)

Is it possible that this is because of the SHA1 implementation being used? In that case, I could try to use another one.

I'm no expert of cryptography, but the OAuth RFC 5849 is saying that RSASSA-PKCS1-V1_5-SIGN needs to be used, which seems to be the case for the library.

Thank you very much.

Gz Zheng Gz Zheng · Accepted Answer · 2012-01-27T16:45:20

I tried both the openssl command and the JS library you mentioned above, and the results are consistent. The signatures that I get from both ways are the same.

One thing I noticed from your post is that, the base64 encoded result generated from the library is way too long and looks wrong. Is it possible that you are not base64-encoding the binary signature?

Could you try this code for getting the base64 encoded string of the signature?

function doSign() {
  var rsa = new RSAKey();
  rsa.readPrivateKeyFromPEMString(document.form1.prvkey1.value); //replace with your private key
  var hSig = rsa.signString("x", "sha1");
  var base64_encoded_signature = hex2b64(hSig);
}

If you compare the value of "base64_encoded_signature" with what you get from the openssl command, they should be the same.

Generating RSA-SHA1 signatures with JavaScript

1 Answers