Synnefo

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import binascii

from synnefo.userdata.asn1 import DerObject, DerSequence

def exportKey(keyobj, format='PEM'):

    """Export the RSA key. A string is returned

    with the encoded public or the private half

    under the selected format.

    format: 'DER' (PKCS#1) or 'PEM' (RFC1421)

    """

    der = DerSequence()

    if keyobj.has_private():

        keyType = "RSA PRIVATE"

        der[:] = [ 0, keyobj.n, keyobj.e, keyobj.d, keyobj.p, keyobj.q,

        keyobj.d % (keyobj.p-1), keyobj.d % (keyobj.q-1),

        keyobj.u ]

    else:

        keyType = "PUBLIC"

        der.append('\x30\x0D\x06\x09\x2A\x86\x48\x86\xF7\x0D\x01\x01\x01\x05\x00')

        bitmap = DerObject('BIT STRING')

        derPK = DerSequence()

        derPK[:] = [ keyobj.n, keyobj.e ]

        bitmap.payload = '\x00' + derPK.encode()

        der.append(bitmap.encode())

    if format=='DER':

        return der.encode()

    if format=='PEM':

        pem = "-----BEGIN %s KEY-----\n" % keyType

        binaryKey = der.encode()

        # Each BASE64 line can take up to 64 characters (=48 bytes of data)

        chunks = [ binascii.b2a_base64(binaryKey[i:i+48]) for i in range(0, len(binaryKey), 48) ]

        pem += ''.join(chunks)

        pem += "-----END %s KEY-----" % keyType

        return pem

    return ValueError("")