The CSP header does not need to be issued.įor example, for the javascript file script.js we define the hash (digest) sha256: Īnd for the CSS styles file style.css we define the hash (digest) sha512: On any page of the site, we organize the loading of an external script/style whose hash must be determined, and indicate the obviously incorrect attribute value integrity=sha256, integrity=sha384 or integrity=sha512. The method is based on a method for checking the integrity of sub-resources using the integrity= attribute, and the good thing is that, in principle, there is no doubt that the hash is correctly calculated, since the browser calculates it itself. The sha256, sha384, and sha512 hash values for style files and scripts can be viewed in the browser console of Google Chrome. The contents of the external file does not need to be transcoded into UTF8, moreover, update() ignores the passed Encoding if the first argument is not a String but the data of type Buffer, TypedArray, or DataView.įor the inline script (its content is in the buffer variable), it needs to be converted to UTF8: crypto.createHash("sha256").update(buffer, 'utf8').digest('base64') Ĭalculation of hashes/digests using the console of the Google Chrome browser For example, for the external file test.js the command would look like cat test.js | openssl dgst -sha256 -binary | openssl base64 -A: #cat test.js | openssl dgst -sha256 -binary | openssl base64 -AĠX/mXwSMKUkzUfv+VIF49SFUDL0crPAnC532AAN4J74=Ĭomputing sha256 for external file: const fs = require('fs') Ĭonst input = fs.readFileSync("/path/to/script.js") Ĭrypto.createHash("sha256").update(input).digest('base64') Īnd make replacements. The sha256, sha384, and sha512 hash values for style files and scripts are easy to see in the unix server console. $hash = base64_encode( hash ('sha512', $file, TRUE) ) Ĭomputing hashes of sha256, sha384 and sha512 files in the unix server console When calculating the hashes inline scripts and inline styles note this nuance.Ĭalculation of sha512 hash for a script from the file /tst/test.js: $file = file_get_contents ($_ SERVER.'/tst/test.js') Abovementioned security feature is a part of Subresource Integrity ( SRI). In this case, the browser checks the/digest hash of the loaded file with the integrity= attribute specified, and ignores the file if hashes does not match. It should be noted that the hash sha256, sha384 or sha512 is suitable not only for the CSP key 'hash_algorithm-value', but also for the integrity=, which is used to check the integrity of scripts and styles loaded from third-party CDNs (Content Delivery Network), for example:
Sha 256 hash calculator how to#
How to gererate the hash value for sha256, sha384 or sha512 encryption algorithms The " -" character is only used to separate the hash algorithm and the hash value. Thus the value of hash itself can only contain the A- Z and a- z chars, 0- 9 digits, + and /. Has sha256 = ' JXsq/1KEtrnrlGozP1V228Z4rNL2pB7MlgpEBBbVnLA=', (the framing tags and are removed when calculating the hash).ĭifference in calculation of hashes of inline scripts/styles and external filesĬSP 3 made a specific comment on the use of hashes (and second time), since hashes are calculated differently for built-in script/style blocks and external script and style files:Īll '-' characters replace with '+', and all '_' characters replace with '/'
Sha 256 hash calculator code#
Has sha256 = ' 1QhCpB/IFWw8Pb/g/IBzIBgErHWG5wrytauZib+UF+g=', and the same code in one line with spaces at the beginning and end: var i = 1 Has sha256 = ' s29H+4vNsSE0M5LT9togkYGlNI6zF5V1EW2iOrQGdX4=', the same code on one line: var i = 1 When generate hashes for Content Security Policy directives, do not include the or tags themselves and note that uppercase letters and white space characters (they also include line breaks) matters, including leading or trailing whitespace. The hash (digest) of the '-' token for javascripts or styles consists of two portions separated by a dash: the encryption algorithm hash source: sha256/sha384 or sha512 used to create the hash and the base64-encoded hash of the script or style.