How to get Hash value for a file with Javascript or Flash?

Question

What I need to do is provide a file browser window on a web page where the user selects the file from his computer, and through javascript (or, if necessary, flash), some hash is returned, such as CRC, MD5 or SHA1. I would prefer not to upload the entire file to the web server, since I expect quite large files to be used in it.

Basically, I create a script that associates these values ​​with META sorts, allowing you to identify files without downloading them completely.

Any idea how I will do this? It would be easy for me to do this on the server side, but, as I said, some fairly large files will be checked, and I do not want to consume too much server bandwidth.

Answer 1

You can do this using Flash, provided that the user has Flash Player 10.

Here is a tutorial

Also: Reading and writing local files in FP10

Answer 2

This is traditionally not possible with JavaScript, but it can happen that the W3 File Upload spec never lights up.

Option available in Firefox 3:

var content= input.files[0].getAsBinary(); 

For other browsers, you will have to revert to Flash and / or server-side hashing.

Here's the JS SHA-1 implementation bonus for you:

 function sha_hexdigest(bytes) { var digest= sha_bytes(sha_calculate(sha_ints(bytes), bytes.length*8)); var digits= '0123456789abcdef'; var hex= ''; for (var i= 0; i<digest.length; i++) { var c= digest.charCodeAt(i); hex+= digits.charAt((c>>4)&0xF) + digits.charAt(c&0xF); } return hex; } function sha_ints(bytes) { while (bytes.length%4!=0) bytes+= '\x00'; var ints= new Array(); for (var i= 0; i<bytes.length; i+= 4) { ints[ints.length]= ( (bytes.charCodeAt(i)&0xFF)<<24 | (bytes.charCodeAt(i+1)&0xFF)<<16 | (bytes.charCodeAt(i+2)&0xFF)<<8 | (bytes.charCodeAt(i+3)&0xFF) ); } return ints; } function sha_bytes(ints) { var bytes= ''; for (var i= 0; i<ints.length; i++) bytes+= String.fromCharCode((ints[i]>>24)&0xFF, (ints[i]>>16)&0xFF, (ints[i]>>8)&0xFF, ints[i]&0xFF) return bytes; } function sha_calculate(ints, bitn) { while (ints.length*32<=bitn) ints[ints.length]= 0; ints[ints.length-1]|= 1<<(31-bitn%32) while (ints.length%16!=14) ints[ints.length]= 0; ints[ints.length]= Math.floor(bitn/0x100000000); ints[ints.length]= bitn&0xFFFFFFFF; var h0= 1732584193, h1= -271733879, h2= -1732584194, h3= 271733878, h4= -1009589776; var a, b, c, d, e, f, k, temp, w= new Array(80); for(var inti= 0; inti<ints.length; inti+= 16) { a= h0; b= h1; c= h2; d= h3; e= h4; for (var i= 0; i<16; i++) w[i]= ints[inti+i]; for (; i<80; i++) w[i]= sha_rol(w[i-3] ^ w[i-8] ^ w[i-14] ^ w[i-16], 1); for(var i= 0; i<80; i++) { switch (Math.floor(i/20)) { case 0: f= sha_add(1518500249, (b & c) | ((~b) & d)); break; case 1: f= sha_add(1859775393, b ^ c ^ d); break; case 2: f= sha_add(-1894007588, (b & c) | (b & d) | (c & d)); break; case 3: f= sha_add(-899497514, b ^ c ^ d); break; } temp= sha_add( sha_add(sha_rol(a, 5), w[i]), sha_add(e, f) ); e= d; d= c; c= b; b= a; a= temp; c= sha_rol(c, 30); } h0= sha_add(h0, a); h1= sha_add(h1, b); h2= sha_add(h2, c); h3= sha_add(h3, d); h4= sha_add(h4, e); } return new Array(h0, h1, h2, h3, h4); } function sha_add(a, b) { var lsw= (a&0xFFFF) + (b&0xFFFF); var msw= (a>>16) + (b>>16) + (lsw>>16); return (msw<<16) | (lsw&0xFFFF); } function sha_rol(n, bits) { return (n<<bits) | (n>>>(32-bits)); } 

Answer 3

With the HTML5 API, you can read files on the local computer, well versed in my solution: Generate a SHA1 file checksum using the HTML5 file APIs in Javascript

Answer 4

This is not possible with Javascript due to the lack of access to the file system. I know that this can be done with Silverlight. Perhaps someone with flash experience may respond.

Answer 5

Browsers (i.e. JavaScript) cannot access the local file system, period. If they could, it would be a security nightmare.