Signing with a ecdh type private key

[ikouchiha47]

I didn't know where to ask this. But I needed to ask.

The problem is after generating public private keys with ecdh, I am trying to use sign.sign and it doesn't seem to work.
At first I just wrapped the alice.getPrivateKey('base64') inside a -----BEGIN EC PRIVATE KEY----- and -----END EC PRIVATE KEY----- but that resulted in asn1 too long

So I split the private key at 64 characters, and that resulted in Error: error:0D0680A8:asn1 encoding routines:ASN1_CHECK_TLEN:wrong tag
I also tried spliting the `alice.generateKeys().toString('base64') and wrapping it in begin end block. But that too results in the same error.

Here are the codes:

try1.js

const crypto = require('crypto');

// Generate Alice's keys...
const alice = crypto.createECDH('secp521r1');
const aliceKeys = alice.generateKeys();

let pKey = `-----BEGIN EC PRIVATE KEY-----\n${aliceKeys.toString('base64').match(/.{1,64}/g).join('\n')}\n-----END EC PRIVATE KEY-----`;

console.log(pKey)

const sign = crypto.createSign('ecdsa-with-SHA1');
sign.update('some data to sign');
console.log(sign.sign(pkey, 'hex'))

try2.js

const alice = crypto.createECDH('secp521r1');
alice.generateKeys();
const alicePKey = alice.getPrivateKey('base64')

let privateKey = `-----BEGIN EC PRIVATE KEY-----\n${alicePKey.match(/.{1,64}/g).join('\n')}\n-----END EC PRIVATE KEY-----`;

console.log(privateKey)

const sign = crypto.createSign('ecdsa-with-SHA1');
sign.update('some data to sign');

console.log(sign.sign(privateKey, 'hex'))

The error being:

crypto.js:286
  var ret = this._handle.sign(toBuf(key), null, passphrase);
                         ^

Error: error:0D0680A8:asn1 encoding routines:ASN1_CHECK_TLEN:wrong tag
    at Sign.sign (crypto.js:286:26)
    at Object.<anonymous> (/home/argentum/dev/dfh.js:15:6)
    at Module._compile (module.js:571:32)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:488:32)
    at tryModuleLoad (module.js:447:12)
    at Function.Module._load (module.js:439:3)
    at Module.runMain (module.js:605:10)
    at run (bootstrap_node.js:423:7)
at startup (bootstrap_node.js:147:9)

But if I generate the pem file like:

openssl ecparam -genkey -name secp521r1 -noout -out ecdsaprivate.pem

which is from where I copied the begin end blocks. And I read the file in ascii and pass that to the sign method. It works like butter.

What am I doing wrong

[bnoordhuis]

.getPrivateKey() returns just the private key, openssl ecparam -genkey writes the private key wrapped in a PEM-encoded ASN.1 container:

$ openssl ecparam -genkey -name secp521r1 -noout | openssl asn1parse
    0:d=0  hl=3 l= 219 cons: SEQUENCE          
    3:d=1  hl=2 l=   1 prim: INTEGER           :01
    6:d=1  hl=2 l=  65 prim: OCTET STRING      [HEX DUMP]:E713D72B75731D8ED64E2EF6DB54E0EB0CD4AC3FE5BF34270E348DD7CDC3D1428A91C0ABF45B89790D9EC5D87DC4768F13DB5164A48DD2B2BF92B545B9936C85B5
   73:d=1  hl=2 l=   7 cons: cont [ 0 ]        
   75:d=2  hl=2 l=   5 prim: OBJECT            :secp521r1
   82:d=1  hl=3 l= 137 cons: cont [ 1 ]        
   85:d=2  hl=3 l= 134 prim: BIT STRING        

That 65 byte octet string is the private key.

Node.js currently has no direct support for constructing that container but there's probably a library for it on npm (asn1.js?) and worst case, you can construct it yourself, the format is not hugely complex.

I'll close this out, see #15116 for the feature request. Please post follow-up questions to the help repo.

[skerit]

Why doesn't the Sign#sign method allow the use of a Buffer to pass along the private key to use? It seems like quite a waste to first add a wrapper Sign#sign needs to unwrap anyway.

[bnoordhuis]

@skerit Just raw bytes doesn't tell you what kind of key it is or what params it has. Look up how many openssl apis start with 'EVP_PKEY_' and you'll get a feel for the phase space. :-)