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PONeed SJCL to make the same encrypted AES 256 output when the PassPhrase is the same
 

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  1. PONeed SJCL to make the same encrypted AES 256 output when the PassPhrase is the same
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    <p>I'm working on uploading file encrypted on the client side using Node.js, and I use SJCL (Stanford Javascript Crypto Library) to encrypt the file with Javascript.</p> <p>But i noticed that the output or the result of the encryption is always different even with the same PassPhrase.</p> <p>After few research i found that it's because the salt is random each time and i need to do a 'nosalt' (sorry I'm new to everything here cryptographie, Node.js)</p> <p>How can I change my code (or SJCL code) to generate the exact encrypt output each time when the password is the same.</p> <p>My app is based on "Cryptloader" project, you can find it here: <a href="https://github.com/Kryil/Cryptloader" rel="nofollow">https://github.com/Kryil/Cryptloader</a></p> <p>Encrypt:</p> <pre><code>var part = file_queue[data["id"]].slice(start, end) var reader = new FileReader() reader.onload = function(e) { var passwd = document.getElementById("password").value console.log("Uploading arraybuffer of size " + e.target.result.byteLength) var i32a = new Int32Array(e.target.result) var out = i32a.toJSONArray() console.log("crypting: " + out) var crypted = sjcl.encrypt(passwd, out) ws.send(JSON.stringify({ "type": "fileslice", "data": {"id": data["id"], "slice": slice, "data": crypted} })) } reader.readAsArrayBuffer(part) </code></pre> <p>Decrypt:</p> <pre><code>var decrypted = sjcl.decrypt(passwd, data["data"]) file_contents[file]["data"].push(new Int32Array(JSON.parse(decrypted))) </code></pre> <p>This is irrelevant question, but not all files upload correctly, some of them produce an error, but when i Change Int32Array to either Int16Array or Int8Array, it works for them but produce error for other files, what causes that and how to fix it. The error:</p> <pre><code>Uncaught RangeError: ArrayBuffer length minus the byteOffset is not a multiple of the element size. (Chrome Latest version, Win 7) </code></pre>
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    1. USHamada Mido
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      1. USAaron
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    1. COWhy do you need that same keys (and plaintexts) produce identical ciphertexts? Do you want to compare them?
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      1. USPaŭlo Ebermann
    2. COYes, I want to use "convergent encryption" in my app to save space, that's why I want to do this, and since the cipher-text is different each time there's no way to compare them
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      1. USHamada Mido
    3. CONormally with convergent encryption you derive a (maybe keyed) hash from the message/file to use as an identifier (and another one as a key). Compare these identifiers, not the whole files. Have a look at the [\[convergent-encryption\]-tag on our sister site Cryptography Stack Exchange](http://crypto.stackexchange.com/questions/tagged/convergent-encryption).
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      1. PONeed SJCL to make the same encrypted AES 256 output when the PassPhrase is the same
      1. USPaŭlo Ebermann
 

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