Invalid Checksum

Question

I have a problem creating a checksum that matches for OpenSSL and iOS' CommonCrypto implementation. I currently have a .plist file that I want to validate using a checksum. What I have done is the following:

openssl dgst -sha256 file.plist
SHA256(file.plist)= a33184700a1f61f80d4a1d092e83457c9abdf794c20daa276bd3e1e8a4ceb55c

Alternatively used the internal shasum function

shasum -a 256 file.plist
a33184700a1f61f80d4a1d092e83457c9abdf794c20daa276bd3e1e8a4ceb55c  file.plist

So I now have the sha256 hash of the file. I will create base64 data that can be used in Swift

echo -n 'a33184700a1f61f80d4a1d092e83457c9abdf794c20daa276bd3e1e8a4ceb55c' | xxd -r -p | base64
ozGEcAofYfgNSh0JLoNFfJq995TCDaona9Ph6KTOtVw=

So right now, I have the hash and I can use that in iOS. Note that I hashed the exact file that is in Xcode's file inspector.

let calculatedHash = Data(base64Encoded: "ozGEcAofYfgNSh0JLoNFfJq995TCDaona9Ph6KTOtVw=")!
let fileURL = Bundle.main.url(forResource: "file", withExtension: "plist")!
let fileData = try! Data(contentsOf: fileURL)

var hash = Data(count: Int(CC_SHA256_DIGEST_LENGTH))
hash.withUnsafeMutableBytes { hashBuffer in
   fileData.withUnsafeBytes { buffer in
        _ = CC_SHA256(buffer.baseAddress!, CC_LONG(buffer.count), hashBuffer.bindMemory(UInt8.self).baseAddress)
   }
}

print(caluclatedHash as NSData)
print(hash as NSData)

// <a3318470 0a1f61f8 0d4a1d09 2e83457c 9abdf794 c20daa27 6bd3e1e8 a4ceb55c>
// <96d172a8 48235f59 66ff2af3 dae8220d df33f0aa 3be78c46 9d5a18e4 9c73aecd>

As you can see, the output is different for the iOS hash. Why is that and how do I solve it?

Thanks in advance!

Craz1k0ek

Security

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Craz1k0ek

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Answer 1

Solved by using a python library.

import plistlib
import hashlib

def calc_hash(file_name):
    try:
        f = open(file_name, 'r')
        f_data = f.read()
        f.close()
        file = plistlib.loads(f_data.encode())
    except (ValueError, Exception) as e:
        print("Failed to load file {}".format(file_name))
        return
    dump = plistlib.dumps(file, fmt=plistlib.FMT_BINARY)
  
    hasher = hashlib.sha256()
    hasher.update(dump)
    digest = hasher.digest()
  
    print("{} {}".format(file_name, digest.hex()))

file_name = str(input('Please enter the relative path to the plist (i.e. path/to/plist.plist):\n'))
calc_hash(file_name)

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Craz1k0ek

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Answer 2

You are getting this property list from your bundle. I suspect that the problem here is that the Xcode build system will convert property list files to a binary format, which changes the checksum. You should dump

fileData

to make sure it matches what you expect.

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eskimo

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Answer 3

Is there a way to prevent that from happening? In direct reply to your answer, I did convert it to binary myself:

plutil -convert binary1 file.plist

Posted by

Craz1k0ek

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Answer 4

Solved by using a python library.

import plistlib
import hashlib

def calc_hash(file_name):
    try:
        f = open(file_name, 'r')
        f_data = f.read()
        f.close()
        file = plistlib.loads(f_data.encode())
    except (ValueError, Exception) as e:
        print("Failed to load file {}".format(file_name))
        return
    dump = plistlib.dumps(file, fmt=plistlib.FMT_BINARY)
  
    hasher = hashlib.sha256()
    hasher.update(dump)
    digest = hasher.digest()
  
    print("{} {}".format(file_name, digest.hex()))

file_name = str(input('Please enter the relative path to the plist (i.e. path/to/plist.plist):\n'))
calc_hash(file_name)

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Craz1k0ek

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Invalid Checksum

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