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import hmac
import hashlib
from flask import url_for, current_app as app
def hmac_creation(stringy):
"""Helper function to create the actual hmac"""
secret = app.config['SECRET_HMAC_CODE']
hmaced = hmac.new(bytearray(secret, "latin-1"),
bytearray(stringy, "utf-8"),
hashlib.sha1)
hm = hmaced.hexdigest()
# ZS: Leaving the below comment here to ask Pjotr about
# "Conventional wisdom is that you don't lose much in terms of security if you throw away up to half of the output."
# http://www.w3.org/QA/2009/07/hmac_truncation_in_xml_signatu.html
hm = hm[:20]
return hm
def data_hmac(stringy):
"""Takes arbitrary data string and appends :hmac so we know data hasn't been tampered with"""
return stringy + ":" + hmac_creation(stringy)
def url_for_hmac(endpoint, **values):
"""Like url_for but adds an hmac at the end to insure the url hasn't been tampered with"""
url = url_for(endpoint, **values)
hm = hmac_creation(url)
if '?' in url:
combiner = "&"
else:
combiner = "?"
return url + combiner + "hm=" + hm
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