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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 crypto_sign_open(signed, vk):
 """Return message given signature+message and the verifying key."""

    if len(vk) != PUBLICKEYBYTES:
        raise ValueError("Bad verifying key length %d" % len(vk))
    rc = djbec.checkvalid(signed[:SIGNATUREBYTES], signed[SIGNATUREBYTES:], vk)
    if not rc:
        raise ValueError("rc != True", rc)
    return signed[SIGNATUREBYTES:]