Get a macOS Keychain certificate's SHA1 hash in Swift - macos

Question

I've retrieved the set of certificates in my keychain using this code:
let query: [String: Any] = [
kSecClass as String: kSecClassCertificate,
kSecMatchLimit as String: kSecMatchLimitAll,
kSecReturnAttributes as String: false,
kSecReturnData as String: true
]
var result: CFTypeRef?
var results : Set<CertsResult> = []
let status = SecItemCopyMatching(query as CFDictionary, &result)
//[Check status]
guard let certificateData = result as? [CFData] else {
//[Handle]
}
From here, I loop through certificateData and gather information about the certificates, but I need to get the SHA1 hash of the certificates as well. I've gathered from researching that I need to use import CommonCrypto and CC_SHA1, but what I've read doesn't use a CFData.
Is there a good way to get from this point to its SHA1?

Answer 1

You can achieve it by performing the hash yourself. The fingerprints are not part of the certificate itself. More info about that over here.
import CryptoKit
let certificate = ...
let der = SecCertificateCopyData(certificate) as Data
let sha1 = Insecure.SHA1.hash(data: der)
let sha256 = SHA256.hash(data: der)
This can be created in an extension too. I've used CommonCrypto in the extension.
import CommonCrypto
extension SecCertificate {
var sha1: Data {
var digest = [UInt8](repeating: 0, count: Int(CC_SHA1_DIGEST_LENGTH))
let der = SecCertificateCopyData(self) as Data
_ = CC_SHA1(Array(der), CC_LONG(der.count), &digest)
return Data(digest)
}
var sha256: Data {
var digest = [UInt8](repeating: 0, count: Int(CC_SHA256_DIGEST_LENGTH))
let der = SecCertificateCopyData(self) as Data
_ = CC_SHA256(Array(der), CC_LONG(der.count), &digest)
return Data(digest)
}
}
I'd like to mention that SHA-1 hashes of certificates are deprecated since like 2017 and websites and tech giants are starting to drop support for them.
Playground example
import CryptoKit
import Foundation
class CertificateStuff: NSObject, URLSessionDelegate {
func urlSession(
_ session: URLSession,
didReceive challenge: URLAuthenticationChallenge,
completionHandler: #escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void
) {
guard let serverTrust = challenge.protectionSpace.serverTrust else {
completionHandler(.rejectProtectionSpace, nil)
return
}
for index in 0 ..< SecTrustGetCertificateCount(serverTrust) {
let certificate = SecTrustGetCertificateAtIndex(serverTrust, index)!
let der = SecCertificateCopyData(certificate)
let sha1 = Insecure.SHA1.hash(data: der as Data)
let sha256 = SHA256.hash(data: der as Data)
print(certificate)
print(sha1)
print(sha256)
print()
}
completionHandler(.performDefaultHandling, nil)
}
func request(_ done: #escaping (Result<Data, Error>) -> Void) {
let url = URL(string: "https://security.stackexchange.com/questions/14330/what-is-the-actual-value-of-a-certificate-fingerprint")!
let request = URLRequest(url: url)
URLSession(configuration: .default, delegate: self, delegateQueue: nil).dataTask(with: request) { (d, r, e) in
if let e = e {
print(e)
return
}
print(d!)
}.resume()
}
}
CertificateStuff().request { result in print(result) }