tlslite/utils/pem.py

# Author: Trevor Perrin
# See the LICENSE file for legal information regarding use of this file.

from .compat import *
import binascii

#This code is shared with tackpy (somewhat), so I'd rather make minimal
#changes, and preserve the use of a2b_base64 throughout.

def dePem(s, name):
    """Decode a PEM string into a bytearray of its payload.
    
    The input must contain an appropriate PEM prefix and postfix
    based on the input name string, e.g. for name="CERTIFICATE":

    -----BEGIN CERTIFICATE-----
    MIIBXDCCAUSgAwIBAgIBADANBgkqhkiG9w0BAQUFADAPMQ0wCwYDVQQDEwRUQUNL
...
    KoZIhvcNAQEFBQADAwA5kw==
    -----END CERTIFICATE-----    

    The first such PEM block in the input will be found, and its
    payload will be base64 decoded and returned.
    """
    prefix  = "-----BEGIN %s-----" % name
    postfix = "-----END %s-----" % name    
    start = s.find(prefix)
    if start == -1:
        raise SyntaxError("Missing PEM prefix")
    end = s.find(postfix, start+len(prefix))
    if end == -1:
        raise SyntaxError("Missing PEM postfix")
    s = s[start+len("-----BEGIN %s-----" % name) : end]
    retBytes = a2b_base64(s) # May raise SyntaxError
    return retBytes
    
def dePemList(s, name):
    """Decode a sequence of PEM blocks into a list of bytearrays.

    The input must contain any number of PEM blocks, each with the appropriate
    PEM prefix and postfix based on the input name string, e.g. for
    name="TACK BREAK SIG".  Arbitrary text can appear between and before and
    after the PEM blocks.  For example:

    " Created by TACK.py 0.9.3 Created at 2012-02-01T00:30:10Z -----BEGIN TACK
    BREAK SIG-----
    ATKhrz5C6JHJW8BF5fLVrnQss6JnWVyEaC0p89LNhKPswvcC9/s6+vWLd9snYTUv
    YMEBdw69PUP8JB4AdqA3K6Ap0Fgd9SSTOECeAKOUAym8zcYaXUwpk0+WuPYa7Zmm
    SkbOlK4ywqt+amhWbg9txSGUwFO5tWUHT3QrnRlE/e3PeNFXLx5Bckg= -----END TACK
    BREAK SIG----- Created by TACK.py 0.9.3 Created at 2012-02-01T00:30:11Z
    -----BEGIN TACK BREAK SIG-----
    ATKhrz5C6JHJW8BF5fLVrnQss6JnWVyEaC0p89LNhKPswvcC9/s6+vWLd9snYTUv
    YMEBdw69PUP8JB4AdqA3K6BVCWfcjN36lx6JwxmZQncS6sww7DecFO/qjSePCxwM
    +kdDqX/9/183nmjx6bf0ewhPXkA0nVXsDYZaydN8rJU1GaMlnjcIYxY= -----END TACK
    BREAK SIG----- "
    
    All such PEM blocks will be found, decoded, and return in an ordered list
    of bytearrays, which may have zero elements if not PEM blocks are found.
     """
    bList = []
    prefix  = "-----BEGIN %s-----" % name
    postfix = "-----END %s-----" % name
    while 1:
        start = s.find(prefix)
        if start == -1:
            return bList
        end = s.find(postfix, start+len(prefix))
        if end == -1:
            raise SyntaxError("Missing PEM postfix")
        s2 = s[start+len(prefix) : end]
        retBytes = a2b_base64(s2) # May raise SyntaxError
        bList.append(retBytes)
        s = s[end+len(postfix) : ]

def pem(b, name):
    """Encode a payload bytearray into a PEM string.
    
    The input will be base64 encoded, then wrapped in a PEM prefix/postfix
    based on the name string, e.g. for name="CERTIFICATE":
    
    -----BEGIN CERTIFICATE-----
    MIIBXDCCAUSgAwIBAgIBADANBgkqhkiG9w0BAQUFADAPMQ0wCwYDVQQDEwRUQUNL
...
    KoZIhvcNAQEFBQADAwA5kw==
    -----END CERTIFICATE-----    
    """
    s1 = b2a_base64(b)[:-1] # remove terminating \n
    s2 = ""
    while s1:
        s2 += s1[:64] + "\n"
        s1 = s1[64:]
    s = ("-----BEGIN %s-----\n" % name) + s2 + \
        ("-----END %s-----\n" % name)     
    return s

def pemSniff(inStr, name):
    searchStr = "-----BEGIN %s-----" % name
    return searchStr in inStr