MD5 hash of blob uploaded on Azure doesnt match with same file on local machine

7
votes

I am currently working on uploading media on Azure Blob storage. All is working fine except when i try to macth the MD5 hash of uploaded media with the local file (exactly same one which was uploaded). Local file returns a byte array where are blob.Properties.ContentMD5 returns a string and both do not match.

Local MD5 hash: sÔ(F¦‚"“Db~[N

blob.Properties.ContentMD5: c9QoHkamgiKTRANifltOGQ==

Any possible way to match both these?

1
c#azurehashmd5azure-storage
Try to convert MD5 byte array into Base64 string and see if that matches. – Gaurav Mantri
It does work! Thanks – Salman

1 Answers

10
votes

Here is a good article on how to calculate and check Blob MD5 checksums.

I have faced this before, and I don't know why, but you can'T just do md5.computeHash(fileBytes). For Azure Blobs, it uses the following path to get the hash:

// Validate MD5 Value
var md5Check = System.Security.Cryptography.MD5.Create();
md5Check.TransformBlock(retrievedBuffer, 0, retrievedBuffer.Length, null, 0);     
md5Check.TransformFinalBlock(new byte[0], 0, 0);

// Get Hash Value
byte[] hashBytes = md5Check.Hash;
string hashVal = Convert.ToBase64String(hashBytes);

and it works...

And yes, as Guarav already mentioned - MD5 hash is saved as base64 string.