Trying to decrypt AES, bad decrypt

[Thijs Koerselman]

Hi,

I'm trying to encrypt some string in C#, send it to a Node server and
decrypt it there. I am having a hard time because I keep getting this error:

TypeError: error:06065064:digital envelope routines:EVP_DecryptFinal_ex:bad
decrypt
at Decipher.Cipher.final (crypto.js:257:27)

I have tried different AES modes and key sizes but it didn't help. Just for
testing I'm sending a json post to the server containing base64 encoded
versions of key, iv and the encrypted string (fingerprint in this example).

In the post request handler I do this:

var crypto = require('crypto');
var key = req.body.key;
var iv = req.body.iv;
var binkey = new Buffer(key, 'base64');
var biniv = new Buffer(iv, 'base64');

var crypted = req.body.fingerprint;
var bincrypted = new Buffer(crypted, 'base64');
var decipher = crypto.createDecipher('aes-256-cbc',binkey, biniv);
var dec = decipher.update(bincrypted,'binary','utf8');
dec += decipher.final('utf8');
console.log("dec", dec);

To be sure I'm using the same Aes mode and padding on the encryption this
is what's reported by my C# Aes, including the JSON being sent.

Keysize 256
Mode CBC
Padding PKCS7
Key: YJAG4xYTTQ0Ke3FBIDgmobERgbi/Tl/LYt9cNmt5w0g=
IV :VUdInSdIlCLS/D3AbXhhnQ==
json: {
"fingerprint" : "a7pNFC3Bnac7Y/k7/b+b4jHdH5CE/nbu23Mmj9pAhZw=",
"key" : "YJAG4xYTTQ0Ke3FBIDgmobERgbi/Tl/LYt9cNmt5w0g=",
"iv" : "VUdInSdIlCLS/D3AbXhhnQ=="
}

Am I overlooking something maybe?
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[Kelsey Dawes]

Hi,

Post by Thijs Koerselman

Post by Thijs Koerselman
var decipher = crypto.createDecipher('aes-256-cbc',binkey, biniv);

I think you want crypto.createDecipheriv here, instead of
crypto.createDecipher.

crypto.createDecipheriv(algorithm, key, iv)
creates and returns a decipher object, with the given algorithm, key and
iv. This is the mirror of
thecreateCipheriv()<http://nodejs.org/api/crypto.html#crypto_crypto_createcipheriv_algorithm_key_iv>
above

-Kelsey

Post by Thijs Koerselman
Hi,
I'm trying to encrypt some string in C#, send it to a Node server and
TypeError: error:06065064:digital envelope
routines:EVP_DecryptFinal_ex:bad decrypt
at Decipher.Cipher.final (crypto.js:257:27)
I have tried different AES modes and key sizes but it didn't help. Just
for testing I'm sending a json post to the server containing base64 encoded
versions of key, iv and the encrypted string (fingerprint in this example).
var crypto = require('crypto');
var key = req.body.key;
var iv = req.body.iv;
var binkey = new Buffer(key, 'base64');
var biniv = new Buffer(iv, 'base64');
var crypted = req.body.fingerprint;
var bincrypted = new Buffer(crypted, 'base64');
var decipher = crypto.createDecipher('aes-256-cbc',binkey, biniv);
var dec = decipher.update(bincrypted,'binary','utf8');
dec += decipher.final('utf8');
console.log("dec", dec);
To be sure I'm using the same Aes mode and padding on the encryption this
is what's reported by my C# Aes, including the JSON being sent.
Keysize 256
Mode CBC
Padding PKCS7
Key: YJAG4xYTTQ0Ke3FBIDgmobERgbi/Tl/LYt9cNmt5w0g=
IV :VUdInSdIlCLS/D3AbXhhnQ==
json: {
"fingerprint" : "a7pNFC3Bnac7Y/k7/b+b4jHdH5CE/nbu23Mmj9pAhZw=",
"key" : "YJAG4xYTTQ0Ke3FBIDgmobERgbi/Tl/LYt9cNmt5w0g=",
"iv" : "VUdInSdIlCLS/D3AbXhhnQ=="
}
Am I overlooking something maybe?
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[Thijs Koerselman]

Post by Kelsey Dawes
I think you want crypto.createDecipheriv here, instead of
crypto.createDecipher.

Ouch! I must have read over that about 30 times. I was assuming the two
flavors were based on the number of arguments you supplied to the same
create function. Thanks for pointing it out. It's working now!

I would prefer to use a password to derive the key from that, and append IV
before the data. That way I can just have one shared password between my
apps. How do I know in what way Node crypto derives that key from the
password so that I can match it in C#? Or the other way around?
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