RSA key format conversions

RSA key format conversions

def pub_to_e_n(key):
    """
    Converts a .pub public key to an exponent and n value
    :param key: String. Public key
    :return: e as Int
    :return: n as Long
    """
    import base64
    import struct
    
    keydata = base64.b64decode(key.split(None)[1])

    parts = []
    while keydata:
        # read the length of the data
        dlen = struct.unpack('>I', keydata[:4])[0]
        # read in <length> bytes
        data, keydata = keydata[4:dlen+4], keydata[4+dlen:]
        parts.append(data)
    
    e_val = eval('0x' + ''.join(['%02X' % struct.unpack('B', x)[0] for x in
        parts[1]]))
    n_val = eval('0x' + ''.join(['%02X' % struct.unpack('B', x)[0] for x in
        parts[2]]))
    
    return e_val, n_val

def der_to_e_n(key):
    """
    Converts a DER public key to an exponent and n value
    :param key: String. Public key
    :return: e as Int
    :return: n as Long
    """
    from Crypto.Util import asn1
    from base64 import b64decode
    key = key.replace("-----BEGIN RSA PUBLIC KEY-----", "")
    key = key.replace("-----END RSA PUBLIC KEY-----", "")
    key = b64decode(key)
    seq = asn1.DerSequence()
    seq.decode(key)
    return int(seq[1]), seq[0]
    
    
def convert_pub_to_der(key):
    """
    Converts a .pub public key to DER format
    :param key: String. Public key
    :return: String. The public key in DER format
    """
    import base64
    from pyasn1.type import univ
    from pyasn1.codec.der import encoder as der_encoder
    
    e_val, n_val = pub_to_e_n(key)
    
    pkcs1_seq = univ.Sequence()
    pkcs1_seq.setComponentByPosition(0, univ.Integer(n_val))
    pkcs1_seq.setComponentByPosition(1, univ.Integer(e_val))
    
    pub_key = '-----BEGIN RSA PUBLIC KEY-----'
    pub_key += base64.encodestring(der_encoder.encode(pkcs1_seq))
    pub_key += '-----END RSA PUBLIC KEY-----'
    return pub_key


def convert_pub_to_pem(key):
    """
    Converts a .pub public key to PEM format
    :param key: String. Public key
    :return: String. The public key in PEM format
    """
    return convert_e_n_to_pem(pub_to_e_n(key))


def convert_der_to_pem(key):
    """
    Converts a DER public key to PEM format
    :param key: String. Public key
    :return: String. The public key in PEM format
    """
    return convert_e_n_to_pem(der_to_e_n(key))

    
def convert_e_n_to_pem(vals):
    e_val, n_val = vals
    from M2Crypto import RSA, BIO, m2
    bne = m2.hex_to_bn(str(hex(e_val)[2:]))
    bnn = m2.hex_to_bn(str(hex(n_val))[:-1][2:])
    e = m2.bn_to_mpi(bne)
    n = m2.bn_to_mpi(bnn)
    rsa = RSA.new_pub_key((e, n))
    bio = BIO.MemoryBuffer()
    rsa.save_key_bio(bio)
    return bio.getvalue()