node.js - NodeJS pre-signed URLs for Secure S3 Downloads - Help w/simple spec -

looking review of flow can pinpoint signing calculation going wrong.

the main issue in generating signing key , signature--the hashing of canonical request seems match reference here http://docs.aws.amazon.com/amazons3/latest/api/sigv4-query-string-auth.html

the sha256hmac , getsignature functions this:

function sha256hmac(key, string, encoding = 'hex') {   return crypto.createhmac('sha256', key).update(string, 'utf8').digest(encoding); };  function getsignature(stringtosign, signingdates) {    const datekey              = sha256hmac('aws4' + s3_secret_key, signingdates.shortdate);   const dateregionkey        = sha256hmac(datekey, s3_region);   const dateregionservicekey = sha256hmac(dateregionkey, s3_service);   const signingkey           = sha256hmac(dateregionservicekey, s3_request_type);    const signature = sha256hmac(signingkey, stringtosign);    return signature;  } 

thanks looking!

the fix:

// remove default hex encoding function sha256hmac(key, string, encoding) {   return crypto.createhmac('sha256', key).update(string, 'utf8').digest(encoding); };  function getsignature(stringtosign, signingdates) {    // not supply encoding argument sha256hmac()   // each of these return buffer   const datekey              = sha256hmac('aws4' + s3_secret_key, signingdates.shortdate);   const dateregionkey        = sha256hmac(datekey, s3_region);   const dateregionservicekey = sha256hmac(dateregionkey, s3_service);   const signingkey           = sha256hmac(dateregionservicekey, s3_request_type);    // output hex encoding here   const signature = sha256hmac(signingkey, stringtosign, 'hex');    return signature;  } 

did not grok https://nodejs.org/api/crypto.html#crypto_hmac_digest_encoding

calculates hmac digest of of data passed using hmac.update(). encoding can 'hex', 'latin1' or 'base64'. if encoding provided string returned; otherwise buffer returned;

the hmac object can not used again after hmac.digest() has been called. multiple calls hmac.digest() result in error being thrown.

wiki