epicyon/httpsig.py

__filename__ = "posts.py"
__author__ = "Bob Mottram"
__credits__ = ['lamia']
__license__ = "AGPL3+"
__version__ = "1.1.0"
__maintainer__ = "Bob Mottram"
__email__ = "bob@freedombone.net"
__status__ = "Production"

# see https://tools.ietf.org/html/draft-cavage-http-signatures-06

try:
    from Cryptodome.PublicKey import RSA
    from Cryptodome.Hash import SHA256
    from Cryptodome.Signature import pkcs1_15
except ImportError:
    from Crypto.PublicKey import RSA
    from Crypto.Hash import SHA256
    # from Crypto.Signature import PKCS1_v1_5
    from Crypto.Signature import pkcs1_15

import base64
from time import gmtime, strftime
import datetime


def messageContentDigest(messageBodyJsonStr: str) -> str:
    msg = messageBodyJsonStr.encode('utf-8')
    digestStr = SHA256.new(msg).digest()
    return base64.b64encode(digestStr).decode('utf-8')


def signPostHeaders(dateStr: str, privateKeyPem: str,
                    nickname: str,
                    domain: str, port: int,
                    toDomain: str, toPort: int,
                    path: str,
                    httpPrefix: str,
                    messageBodyJsonStr: str) -> str:
    """Returns a raw signature string that can be plugged into a header and
    used to verify the authenticity of an HTTP transmission.
    """
    if port:
        if port != 80 and port != 443:
            if ':' not in domain:
                domain = domain + ':' + str(port)

    if toPort:
        if toPort != 80 and toPort != 443:
            if ':' not in toDomain:
                toDomain = toDomain + ':' + str(port)

    if not dateStr:
        dateStr = strftime("%a, %d %b %Y %H:%M:%S %Z", gmtime())
    keyID = httpPrefix + '://' + domain + '/users/' + nickname + '#main-key'
    if not messageBodyJsonStr:
        headers = {
            '(request-target)': f'post {path}',
            'host': toDomain,
            'date': dateStr,
            'content-type': 'application/json'
        }
    else:
        bodyDigest = messageContentDigest(messageBodyJsonStr)
        contentLength = len(messageBodyJsonStr)
        headers = {
            '(request-target)': f'post {path}',
            'host': toDomain,
            'date': dateStr,
            'digest': f'SHA-256={bodyDigest}',
            'content-type': 'application/activity+json',
            'content-length': str(contentLength)
        }
    privateKeyPem = RSA.import_key(privateKeyPem)
    # headers.update({
    #     '(request-target)': f'post {path}',
    # })
    # build a digest for signing
    signedHeaderKeys = headers.keys()
    signedHeaderText = ''
    for headerKey in signedHeaderKeys:
        signedHeaderText += f'{headerKey}: {headers[headerKey]}\n'
    signedHeaderText = signedHeaderText.strip()
    headerDigest = SHA256.new(signedHeaderText.encode('ascii'))

    # Sign the digest
    rawSignature = pkcs1_15.new(privateKeyPem).sign(headerDigest)
    signature = base64.b64encode(rawSignature).decode('ascii')

    # Put it into a valid HTTP signature format
    signatureDict = {
        'keyId': keyID,
        'algorithm': 'rsa-sha256',
        'headers': ' '.join(signedHeaderKeys),
        'signature': signature
    }
    signatureHeader = ','.join(
        [f'{k}="{v}"' for k, v in signatureDict.items()])
    return signatureHeader


def createSignedHeader(privateKeyPem: str, nickname: str,
                       domain: str, port: int,
                       toDomain: str, toPort: int,
                       path: str, httpPrefix: str, withDigest: bool,
                       messageBodyJsonStr: str) -> {}:
    """Note that the domain is the destination, not the sender
    """
    contentType = 'application/activity+json'
    headerDomain = toDomain

    if toPort:
        if toPort != 80 and toPort != 443:
            if ':' not in headerDomain:
                headerDomain = headerDomain + ':' + str(toPort)

    dateStr = strftime("%a, %d %b %Y %H:%M:%S %Z", gmtime())
    if not withDigest:
        headers = {
            '(request-target)': f'post {path}',
            'host': headerDomain,
            'date': dateStr
        }
        signatureHeader = \
            signPostHeaders(dateStr, privateKeyPem, nickname,
                            domain, port, toDomain, toPort,
                            path, httpPrefix, None)
    else:
        bodyDigest = messageContentDigest(messageBodyJsonStr)
        contentLength = len(messageBodyJsonStr)
        headers = {
            '(request-target)': f'post {path}',
            'host': headerDomain,
            'date': dateStr,
            'digest': f'SHA-256={bodyDigest}',
            'content-length': str(contentLength),
            'content-type': contentType
        }
        signatureHeader = \
            signPostHeaders(dateStr, privateKeyPem, nickname,
                            domain, port,
                            toDomain, toPort,
                            path, httpPrefix, messageBodyJsonStr)
    headers['signature'] = signatureHeader
    return headers


def verifyRecentSignature(signedDateStr: str) -> bool:
    """Checks whether the given time taken from the header is within
    12 hours of the current time
    """
    currDate = datetime.datetime.utcnow()
    dateFormat = "%a, %d %b %Y %H:%M:%S %Z"
    signedDate = datetime.datetime.strptime(signedDateStr, dateFormat)
    timeDiffSec = (currDate - signedDate).seconds
    # 12 hours tollerance
    if timeDiffSec > 43200:
        print('WARN: Header signed too long ago: ' + signedDateStr)
        print(str(timeDiffSec / (60 * 60)) + ' hours')
        return False
    if timeDiffSec < 0:
        print('WARN: Header signed in the future! ' + signedDateStr)
        print(str(timeDiffSec / (60 * 60)) + ' hours')
        return False
    return True


def verifyPostHeaders(httpPrefix: str, publicKeyPem: str, headers: dict,
                      path: str, GETmethod: bool,
                      messageBodyDigest: str,
                      messageBodyJsonStr: str, debug: bool) -> bool:
    """Returns true or false depending on if the key that we plugged in here
    validates against the headers, method, and path.
    publicKeyPem - the public key from an rsa key pair
    headers - should be a dictionary of request headers
    path - the relative url that was requested from this site
    GETmethod - GET or POST
    messageBodyJsonStr - the received request body (used for digest)
    """

    if GETmethod:
        method = 'GET'
    else:
        method = 'POST'

    if debug:
        print('DEBUG: verifyPostHeaders ' + method)

    publicKeyPem = RSA.import_key(publicKeyPem)
    # Build a dictionary of the signature values
    signatureHeader = headers['signature']
    signatureDict = {
        k: v[1:-1]
        for k, v in [i.split('=', 1) for i in signatureHeader.split(',')]
    }

    # Unpack the signed headers and set values based on current headers and
    # body (if a digest was included)
    signedHeaderList = []
    for signedHeader in signatureDict['headers'].split(' '):
        if debug:
            print('DEBUG: verifyPostHeaders signedHeader=' + signedHeader)
        if signedHeader == '(request-target)':
            appendStr = f'(request-target): {method.lower()} {path}'
            signedHeaderList.append(appendStr)
        elif signedHeader == 'digest':
            if messageBodyDigest:
                bodyDigest = messageBodyDigest
            else:
                bodyDigest = messageContentDigest(messageBodyJsonStr)
            signedHeaderList.append(f'digest: SHA-256={bodyDigest}')
        elif signedHeader == 'content-length':
            if headers.get(signedHeader):
                appendStr = f'content-length: {headers[signedHeader]}'
                signedHeaderList.append(appendStr)
            else:
                if headers.get('Content-Length'):
                    contentLength = headers['Content-Length']
                    signedHeaderList.append(f'content-length: {contentLength}')
                else:
                    if headers.get('Content-length'):
                        contentLength = headers['Content-length']
                        appendStr = f'content-length: {contentLength}'
                        signedHeaderList.append(appendStr)
                    else:
                        if debug:
                            print('DEBUG: verifyPostHeaders ' + signedHeader +
                                  ' not found in ' + str(headers))
        else:
            if headers.get(signedHeader):
                if signedHeader == 'date':
                    if not verifyRecentSignature(headers[signedHeader]):
                        if debug:
                            print('DEBUG: ' +
                                  'verifyPostHeaders date is not recent ' +
                                  headers[signedHeader])
                        return False
                signedHeaderList.append(
                    f'{signedHeader}: {headers[signedHeader]}')
            else:
                signedHeaderCap = signedHeader.capitalize()
                if signedHeaderCap == 'Date':
                    if not verifyRecentSignature(headers[signedHeaderCap]):
                        if debug:
                            print('DEBUG: ' +
                                  'verifyPostHeaders date is not recent ' +
                                  headers[signedHeader])
                        return False
                if headers.get(signedHeaderCap):
                    signedHeaderList.append(
                        f'{signedHeader}: {headers[signedHeaderCap]}')

    if debug:
        print('DEBUG: signedHeaderList: ' + str(signedHeaderList))
    # Now we have our header data digest
    signedHeaderText = '\n'.join(signedHeaderList)
    headerDigest = SHA256.new(signedHeaderText.encode('ascii'))

    # Get the signature, verify with public key, return result
    signature = base64.b64decode(signatureDict['signature'])

    try:
        pkcs1_15.new(publicKeyPem).verify(headerDigest, signature)
        return True
    except (ValueError, TypeError):
        if debug:
            print('DEBUG: verifyPostHeaders pkcs1_15 verify failure')
        return False