WebCrypto: Importing rsa public key with modulus and exponent using crypto.subtle.importKey

Question

I generated rsa key by jsbn:

{
  "e": "10001",
  "n": "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",
  ...}

"e" is exponent and "n" is the modulus

And I want to import it using crypto.subtle.importKey.

This is the error that I find:

DOMException: The JWK member "n" could not be base64url decoded or contained padding

Does anybody know where is the problem?

Look at the my code below.

var keyData = {
    kty: 'RSA',
    e: hexToBase64(rsaJson.e),
    n: hexToBase64(rsaJson.n),
    alg: 'RSA-OAEP-256',
    ext: true
};
 
var algo = {
    name: 'RSA-OAEP',
    hash: {name: 'SHA-256'}
};

var importedKey = crypto.subtle.importKey('jwk', keyData, algo, false, ['encrypt']).catch(function(err) {
         console.log(err);
     }); 

Answer 1

You need to provide a JWK key with values encoded in base64url which is slightly different from base64. Convert the result of hexToBase64 to base64url encoding

This code will work

var keyData = {
    kty: 'RSA',
    e: b64tob64u(hexToBase64(rsaJson.e)),
    n: b64tob64u(hexToBase64(rsaJson.n)),
    alg: 'RSA-OAEP-256',
    ext: true
};

var algo = {
    name: 'RSA-OAEP',
    hash: {name: 'SHA-256'}
};

crypto.subtle.importKey('jwk', keyData, algo, false, ['encrypt'])
.then (function (importedKey){
    console.log(importedKey);
}).catch(function(err) {
    console.log(err);
}); 

---

function b64tob64u(a){
    a=a.replace(/\=/g,"");
    a=a.replace(/\+/g,"-");
    a=a.replace(/\//g,"_");
    return a
}

Note also WebCryptographyApi works with promises and is async. I changed

var importedKey = crypto.subtle.importKey(params...)

with

crypto.subtle.importKey(params...).then (function (importedKey)