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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 decrypt(source, dest=None, passphrase=None):
 """Attempts to decrypt a file"""

    if not os.path.exists(source):
        raise CryptoritoError("Encrypted file %s not found" % source)

    cmd = [gnupg_bin(), gnupg_verbose(), "--decrypt", gnupg_home(),
           passphrase_file(passphrase)]

    if dest:
        cmd.append(["--output", dest])

    cmd.append([source])
    stderr_output(flatten(cmd))
    return True