CODEWITHSUNDEEP
c#hashsha512
musium
musium

Reputation: 3072

Hashvalue from SHA512 algorithm is 128 bits long?

I’ve a strange problem. In my code I create a sha512 hash algorithm and sign some data with it. Now I would expect the hash to be 512 bits long, but it’s 128. What mistake have I made?

My Code:

var hashAlgorithm = HashAlgorithm.Create( „SHA512“ );
var signedhHash = rsaCryptoServiceProvider.SignData( plainData, hashAlgorithm );

PS. I’ve loaded the RSA keys from a file, which I’ve created with the following script:

makecert -r -n "CN=myCert" -sky exchange -sy 24 -sv myCert.pvk myCert.cer
cert2spc myCert.cer myCert.spc
pvk2pfx -pvk myCert.pvk -spc myCert.spc -pfx myCert.pfx –f

Edit:

I got the length from signedhHash.Length, which is equal to 128.

Upvotes: 4

Views: 1278

Answers (2)

Magnus
Magnus

Reputation: 46947

The hash value is 512 in size, but the signed hash value (from SignData) is 1024 in size.

var alg = HashAlgorithm.Create("SHA512");
var hashArr = alg.ComputeHash(ASCIIEncoding.UTF8.GetBytes("test"));
var size = hashArr.Length * 8; //512

var rsaCryptoServiceProvider = new RSACryptoServiceProvider();
var signedValue = rsaCryptoServiceProvider.SignData(ASCIIEncoding.UTF8.GetBytes("test"), alg);
size = signedValue.Length * 8; //1024

(1 byte = 8 bits)

Upvotes: 3

HasaniH
HasaniH

Reputation: 8402

The SignData does not return the hash made with the SHA512 algorithm it returns the signature for that hash made with the SignatureAlgorithm property of the provider (http://www.w3.org/2000/09/xmldsig#rsa-sha1)

Upvotes: 0

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