B4X

Compute a Private Key's JWK Thumbprint

Demonstrates the Chilkat PrivateKey.GetJwkThumbprint method, which computes the RFC 7638 thumbprint of the key's public portion using a named hash algorithm. The only argument is the hash algorithm (for example sha256).

Note: The file paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: A JWK thumbprint is a stable, canonical hash of a key's public parameters — a short fingerprint that identifies the key independent of formatting. It is widely used as a key ID (kid) in JWK Sets and JWTs, and for comparing whether two representations are the same key. Because it hashes only the public portion, it can be shared freely even though it is computed here from the private key.

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Dim success As Boolean = False

'  Load a private key to export.
Dim privKey As ChilkatPrivateKey
privKey.Initialize("privKey")
success = privKey.LoadPemFile("qa_data/private.pem")
If success = False Then
    Log(privKey.LastErrorText)
    Return
End If


'  Compute the RFC 7638 thumbprint of the key's public portion using the named hash algorithm.
'  Supported values include "sha256", "sha1", "md5", and others.
Dim thumbprint As String = privKey.GetJwkThumbprint("sha256")
If privKey.LastMethodSuccess = False Then
    Log(privKey.LastErrorText)
    Return
End If

Log("JWK thumbprint: " & thumbprint)