# Utility functions for a Python SSL certificate conversion tool. # These functions are in this file so the can also be used in # A web API implementing this tool. # Author: Tony DiCola, Modified by Noah Koontz # # Dependencies: # click - Install with 'sudo pip install click' (omit sudo on windows) # PyOpenSSL - See homepage: https://pyopenssl.readthedocs.org/en/latest/ # Should just be a 'sudo pip install pyopenssl' command, HOWEVER # on Windows you probably need a precompiled binary version. Try # installing with pip and if you see errors when running that # OpenSSL can't be found then try installing egenix's prebuilt # PyOpenSSL library and OpenSSL lib: # http://www.egenix.com/products/python/pyOpenSSL/ # certifi - Install with 'sudo pip install certifi' (omit sudo on windows) import re from OpenSSL import SSL, crypto import socket import textwrap import math import os CERT_PATTERN = re.compile("^\-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-[a-z,A-Z,0-9,\n,\/,+]+={0,2}\n\-\-\-\-\-END CERTIFICATE-\-\-\-\-", re.MULTILINE) # Default name prefixes for varibles used in the hearder autogeneration # Autogenerator will follow these names with a number # e.g. "TA_DN0" # Distinguished name array prefix DN_PRE = "TA_DN" # RSA public key number prefix RSA_N_PRE = "TA_RSA_N" # RSA public key exponent prefix RSA_E_PRE = "TA_RSA_E" # Template that defines the C header output format. # This takes in a few named parameters: # - guard_name: Unique name to apply to the #ifndef header guard. # - cert_length_var: Variable/define name for the length of the certificate. # - cert_length: Length of the certificate (in bytes). # - cert_var: Variable name for the certificate data. # - cert_data: Certificate data, formatted as a bearssl trust anchor array # - cert_description: Any descriptive info about the certs to put in comments. # NOTE: If you're changing the template make sure to escape all curly braces # with a double brace (like {{ or }}) or else Python will try to interpret as a # string format variable. CFILE_TEMPLATE = """\ #ifndef _{guard_name}_H_ #define _{guard_name}_H_ #ifdef __cplusplus extern "C" {{ #endif /* This file is auto-generated by the pycert_bearssl tool. Do not change it manually. * Certificates are BearSSL br_x509_trust_anchor format. Included certs: * {cert_description} */ #define {cert_length_var} {cert_length} {cert_data} #ifdef __cplusplus }} /* extern "C" */ #endif #endif /* ifndef _{guard_name}_H_ */ """ # Template that defines a static array of bytes # This takes in a few named parameters: # - ray_type: The type (int, unsigned char) to use for the static array # - ray_name: The varible name of the static array # - ray_data: The comma seperated data of the array (ex. "0x12, 0x34, ...") CRAY_TEMPLATE = """\ static const {ray_type} {ray_name}[] = {{ {ray_data} }};""" # Template that defines a single root certificate entry in the BearSSL trust # anchor list # This takes in a few named parameters: # - ta_dn_name: The name of the static byte array containing the distunguished # name of the certificate. # - rsa_number_name: Varible name of the static array containing the RSA number # - rsa_exp_name: Varible name of the static array containing the RSA exponent CROOTCA_TEMPLATE = """\ {{ {{ (unsigned char *){ta_dn_name}, sizeof {ta_dn_name} }}, BR_X509_TA_CA, {{ BR_KEYTYPE_RSA, {{ .rsa = {{ (unsigned char *){rsa_number_name}, sizeof {rsa_number_name}, (unsigned char *){rsa_exp_name}, sizeof {rsa_exp_name}, }} }} }} }},""" # Template that defines a description of the certificate, so that the header # file can be slightly more human readable # This takes in a few named parameters: # - cert_num: The index used to represent the certificate to the computer # - cert_label: The certificate's name field (Usually CN, in the subject) # - cert_issue: The certificate's issuer string # - cert_subject: The certificate's subject string CCERT_DESC_TEMPLATE = """\ * Index: {cert_num} * Label: {cert_label} * Subject: {cert_subject}""" def PEM_split(cert_pem): """Split a certificate / certificate chain in PEM format into multiple PEM certificates. This is useful for extracting the last / root PEM cert in a chain for example. Will return a list of strings with each string being an individual PEM certificate (including its '-----BEGIN CERTIFICATE...' delineaters). """ # Split cert based on begin certificate sections, then reconstruct as an # array of individual cert strings. return re.findall(CERT_PATTERN, cert_pem) def parse_root_certificate_store(store): """Parses a list of trusted root certificates, which we can match to the respective certificates sent from the websites. The where parameter takes a loaded certificate file (certifi.where()), and the function returns a list of crypto.x509 objects. """ # perform file operations certStore = PEM_split(store.read()) # convert the raw PEM files into x509 object return [crypto.load_certificate(crypto.FILETYPE_PEM, pem) for pem in certStore] def get_server_root_cert(address, port, certDict): """Attempt to retrieve the the root certificate in the full SSL cert chain from the provided server address & port. The certDict parameter should contain a dictionary of { certificate.get_subject().hash() md5 hash : certificate }, which this function will use to match the certificate chain to a stored root certificate. This function will return a single certificate as a PyOpenSSL X509 object, or None if the chain couldn't be retrieved for some reason, or the certDict did not contain a matching certificate. """ # Use PyOpenSSL to initiate an SSL connection and get the full cert chain. # Sadly Python's built in SSL library can't do this so we must use this # OpenSSL-based library. cert = None ctx = SSL.Context(SSL.TLSv1_2_METHOD) # do the connection, and fetch the cert chain soc = socket.socket(socket.AF_INET, socket.SOCK_STREAM) ssl_soc = SSL.Connection(ctx, soc) ssl_soc.connect((address, port)) try: ssl_soc.do_handshake() cert = ssl_soc.get_peer_cert_chain()[-1] finally: ssl_soc.shutdown() soc.close() # match the certificate in the chain to the respective root certificate using the common name if cert == None: print("Failed to fetch certificate on domain: " + address) return None cn_hash = cert.get_issuer().hash() # if there is a respective certificate, return it # else print an error and return None if cn_hash not in certDict: print("Could not find matching root certificate for domain: " + address) return None return certDict[cn_hash] def filter_duplicate_x509(certs): serial_numbers = set() out_certs = list() # filter duplicate certs for cert in certs: # Skip duplicate certs where required. if cert.get_serial_number() in serial_numbers: continue out_certs.append(cert) serial_numbers.add(cert.get_serial_number()) return out_certs def bytes_to_c_data(mah_bytes, length=None): """Converts a byte array to a CSV C array data format, with endlines! e.g: 0x12, 0xA4, etc. mah_bytes is the bytearray, and length is the number of bytes to generate in the array, and indent is how much to indent the output """ ret = [] # create an array of byte strings, including an endline every 10 or so bytes for i, bytestr in enumerate(textwrap.wrap(mah_bytes.hex(), 2)): ret.append("0x" + bytestr + ", ") # pad with extra zeros while length != None and len(ret) < length: ret.append("0x00, ") # join, wrap, and return return textwrap.fill(''.join(ret), width=6*12 + 5, initial_indent=' ', subsequent_indent=' ', break_long_words=False) def decribe_cert_object(cert, cert_num): # get the label from the subject feild on the certificate label = "" com = dict(cert.get_subject().get_components()) if b'CN' in com: label = com[b'CN'].decode("utf-8") elif b'OU' in com: label = com[b'OU'].decode("utf-8") elif b'O' in com: label = com[b'O'].decode("utf-8") # return the formated string crypto = cert.to_cryptography() return CCERT_DESC_TEMPLATE.format( cert_num=cert_num, cert_label=label, cert_subject=crypto.subject.rfc4514_string(), ) def x509_to_header(x509Certs, cert_var, cert_length_var, output_file, keep_dupes): """Combine a collection of PEM format certificates into a single C header with the combined cert data in BearSSL format. x509Certs should be a list of pyOpenSSL x590 objects, cert_var controls the name of the cert data variable in the output header, cert_length_var controls the name of the cert data length variable/define, output is the output file (which must be open for writing). Keep_dupes is a boolean to indicate if duplicate certificates should be left intact (true) or removed (false). """ cert_description = '' certs = x509Certs if not keep_dupes: certs = filter_duplicate_x509(x509Certs) # Save cert data as a C style header. # start by building each component cert_data = "" static_arrays = list() CAs = list() cert_desc = list() for i, cert in enumerate(certs): # add a description of the certificate to the array cert_desc.append(decribe_cert_object(cert, i)) # build static arrays containing all the keys of the certificate # start with distinguished name # get the distinguished name in bytes dn_bytes_str = bytes_to_c_data(cert.get_subject().der()) static_arrays.append(CRAY_TEMPLATE.format( ray_type="unsigned char", ray_name=DN_PRE + str(i), ray_data=dn_bytes_str)) # next, the RSA public numbers pubkey = cert.get_pubkey() numbers = pubkey.to_cryptography_key().public_numbers() # starting with the modulous n_bytes_str = bytes_to_c_data(numbers.n.to_bytes(pubkey.bits() // 8, byteorder="big")) static_arrays.append(CRAY_TEMPLATE.format( ray_type="unsigned char", ray_name=RSA_N_PRE + str(i), ray_data=n_bytes_str)) # and then the exponent e_bytes_str = bytes_to_c_data(numbers.e.to_bytes(math.ceil(numbers.e.bit_length() / 8), byteorder="big")) static_arrays.append(CRAY_TEMPLATE.format( ray_type="unsigned char", ray_name=RSA_E_PRE + str(i), ray_data=e_bytes_str)) # format the root certificate entry CAs.append(CROOTCA_TEMPLATE.format( ta_dn_name=DN_PRE + str(i), rsa_number_name=RSA_N_PRE + str(i), rsa_exp_name=RSA_E_PRE + str(i))) # concatonate it all into the big header file template # cert descriptions cert_desc_out = '\n * \n'.join(cert_desc) # static arrays cert_data_out = '\n\n'.join(static_arrays) cert_data_out += '\n\n' + CRAY_TEMPLATE.format( ray_type="br_x509_trust_anchor", ray_name=cert_var, ray_data='\n'.join(CAs)) # create final header file output_file.write(CFILE_TEMPLATE.format( guard_name=os.path.splitext(output_file.name)[0].upper(), cert_description=cert_desc_out, cert_length_var=cert_length_var, cert_length=str(len(certs)), cert_data=cert_data_out, ))