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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def decode_csr(b64der):
 """ Decode JOSE Base-64 DER-encoded CSR. :param str b64der: The encoded CSR. :rtype: `cryptography.x509.CertificateSigningRequest` :return: The decoded CSR. """

    try:
        return x509.load_der_x509_csr(
            decode_b64jose(b64der), default_backend())
    except ValueError as error:
        raise DeserializationError(error)