Node-jsonwebtoken: error:04075070:rsa routines:RSA_sign:digest too big for rsa key

Created on 18 Aug 2020 · 6Comments · Source: auth0/node-jsonwebtoken

Description

I can get HS512 to work, but when I switch to RS512, I get error:04075070:rsa routines:RSA_sign:digest too big for rsa key. I get the same error whether using RS256 or RS512.

Reproduction

My code is this:

const jwt = require("jsonwebtoken");

const token = jwt.sign({ sub: 1 }, "...", { expiresIn: '7d', algorithm: "RS512" });

Environment

Version of this library used: 8.5.1
Version of the platform or framework used, if applicable:
Other relevant versions (language, server software, OS, browser): Node in Windows
Other modules/plugins/libraries that might be involved: express-jwt

Source

RevealedFrom

Most helpful comment

Your RSA key is of insufficient bit length. 2048 bits is minimum required by the JWA specification.

Furthermore, don't sign with HS* using an RSA key :)

panva on 19 Aug 2020

👍3

All 6 comments

Your RSA key is of insufficient bit length. 2048 bits is minimum required by the JWA specification.

Furthermore, don't sign with HS* using an RSA key :)

panva on 19 Aug 2020

👍3

Actually I'm getting the exact same issue (Node 15, Ubuntu)

Here's an example with a random private key:

```-----BEGIN RSA PRIVATE KEY-----
MIIBOgIBAAJBAKrNEPQdc2yJURauXDa2Yu2KLj6sHkM3EDMWrHEC/4RKdrMt9qFl
Hm11YoQRYIm2v/mtdBjrg+FD+MnaEtChYFkCAwEAAQJAX2YsqvzsJFpKVW3MCa8z
cFP24oCGYqqVvMNUS8cN6tgzm5XBZIuc7c2NQ+XzG7xGmvkklbTtKGCkBlrJHJ8L
AQIhAPfjw4kaK1RPga10Cc/+s4QGIRJUPsICBwVY2fFUDMk5AiEAsGOil+vUDr35
yMKod0NwCbUubukGHX/x6fxyY38G8CECIFtjM7Y62JiHizZIHkn5C3Nz0wNv3Ycm
ujHldMu8gc45AiEAg+6SP+WxoDEycpo+na4AUBKHn4eF/myjiis7d/YcP2ECIFnv
bdO+HrfCgkAcbMw0d2pEisYXfZWkAW8q9NJ4OyMp
-----END RSA PRIVATE KEY-----

yields:
Error: error:04075070:rsa routines:RSA_sign:digest too big for rsa key

Stack trace:

at Sign.sign (node:internal/crypto/sig:124:29)
aebc7411959c_web | at Object.sign (/srv/www/node_modules/jwa/index.js:152:45)
aebc7411959c_web | at Object.jwsSign [as sign] (/srv/www/node_modules/jws/lib/sign-stream.js:32:24)
aebc7411959c_web | at Object.module.exports [as sign] (/srv/www/node_modules/jsonwebtoken/sign.js:204:16)
aebc7411959c_web | at /srv/www/main.js:101:35
aebc7411959c_web | at Query. (/srv/www/db.js:45:17)
aebc7411959c_web | at Query. (/srv/www/node_modules/mysql/lib/Connection.js:526:10)
aebc7411959c_web | at Query._callback (/srv/www/node_modules/mysql/lib/Connection.js:488:16)
aebc7411959c_web | at Query.Sequence.end (/srv/www/node_modules/mysql/lib/protocol/sequences/Sequence.js:83:24)
aebc7411959c_web | at Query._handleFinalResultPacket (/srv/www/node_modules/mysql/lib/protocol/sequences/Query.js:149:8) {

So I'm assuming it may be rather a nodejs bug ?

const token = jwt.sign( tokenPayload, myprivateKey, { algorithm: 'RS512', audience: req.params.uid } );
```

NPellet on 18 Jan 2021

So I'm assuming it may be rather a nodejs bug ?

What makes you assume that? Your random private key's modulus length is 512 bits. Insufficient. JWA specification mandates a minimum of 2048. Your issue is the same as the OP's and so should be the answer.

panva on 18 Jan 2021

Hmmm so I can make sure I understand (as I don't know anything about cryptography), what is the relation (if any) between the algorithm (RS512, RS256) I would choose and the modulus length ?

I can sign my token with, say, the RS256 algorithm and a modulus of 2048, if I wanted ? That is, they don't need to match

NPellet on 18 Jan 2021

modulus is one of the components of your RSA private key, its length must be 2048 bits to be universally usable with JOSE. Your key's bit length is 512, generate a key of size 2048 and you'll be able to use all RSA based signing algorithms (it doesn't matter what the algorithm's "number" is since that only dictates the hash algorithm).

Example random 2048 bit RSA private key (click to expand)

panva on 18 Jan 2021

Okaaay that certainly explains a lot. Thank you very much !

On Mon, 18 Jan 2021, 20:54 Filip Skokan, notifications@github.com wrote:

modulus is one of the components of your RSA private key, its length must
be 2048 to be universally usable with JOSE. Your key's bit length is 512,
generate a key of size 2048 and you'll be able to use all RSA based signing
algorithms (it doesn't matter what the algorithm's "number" is since that
only dictates the hash algorithm).
Example random 2048 bit RSA private key (click to expand)

-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----

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