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Created October 23, 2018 05:33
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Function that calculates AWS signature version 4 headers
import datetime
import hashlib
import hmac
import urllib.parse
def aws_sig_v4_headers(access_key_id, secret_access_key, pre_auth_headers,
service, region, host, method, path, query, payload):
algorithm = 'AWS4-HMAC-SHA256'
now = datetime.datetime.utcnow()
amzdate = now.strftime('%Y%m%dT%H%M%SZ')
datestamp = now.strftime('%Y%m%d')
payload_hash = hashlib.sha256(payload).hexdigest()
credential_scope = f'{datestamp}/{region}/{service}/aws4_request'
pre_auth_headers_lower = {
header_key.lower(): ' '.join(header_value.split())
for header_key, header_value in pre_auth_headers.items()
required_headers = {
'host': host,
'x-amz-content-sha256': payload_hash,
'x-amz-date': amzdate,
headers = {**pre_auth_headers_lower, **required_headers}
header_keys = sorted(headers.keys())
signed_headers = ';'.join(header_keys)
def signature():
def canonical_request():
canonical_uri = urllib.parse.quote(path, safe='/~')
quoted_query = sorted(
(urllib.parse.quote(key, safe='~'), urllib.parse.quote(value, safe='~'))
for key, value in query.items()
canonical_querystring = '&'.join(f'{key}={value}' for key, value in quoted_query)
canonical_headers = ''.join(f'{key}:{headers[key]}\n' for key in header_keys)
return f'{method}\n{canonical_uri}\n{canonical_querystring}\n' + \
def sign(key, msg):
return, msg.encode('utf-8'), hashlib.sha256).digest()
string_to_sign = f'{algorithm}\n{amzdate}\n{credential_scope}\n' + \
date_key = sign(('AWS4' + secret_access_key).encode('utf-8'), datestamp)
region_key = sign(date_key, region)
service_key = sign(region_key, service)
request_key = sign(service_key, 'aws4_request')
return sign(request_key, string_to_sign).hex()
return {
'x-amz-date': amzdate,
'x-amz-content-sha256': payload_hash,
'Authorization': f'{algorithm} Credential={access_key_id}/{credential_scope}, '
f'SignedHeaders={signed_headers}, Signature=' + signature(),
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