I think I've read nearly everything there is to read on base-64 encoding of a signature for in-browser, form-based post to S3: old docs and new docs. For instance:
http://doc.s3.amazonaws.com/proposals/post.html
And even found this:
http://s3.amazonaws.com/doc/s3-example-code/post/post_sample.html
Rather than using the above or Amazon's newer policy generator, or fiddle around with Boto, I'm trying to draft a simpler .py script that pulls the policy JSON from a plaintext file (policy.txt), and then generates the necessary base-64 encoded signature to help me draft the HTML form.
The signature itself (which is reliant on the encoded policy) is NOT being encoded correctly...maybe due to some sort of utf-8 vs. ascii or \n (newline) issue?
The script I'm working with is below, the policy and the AWS Secret Key private_key
are from an AWS test case I'm using to see if this script works. The correctly encoded signature--as quoted by Amazon--is included in the script below for reference.
Can anyone tell me why the signature as calculated below does not match the reference signature provided by Amazon?:
In other words:
Why this is correctly encoded:
policy_encoded = base64.b64encode(policy)
but this one is NOT:
signature = base64.b64encode(hmac.new(private_key, policy_encoded, sha).digest())
PYTHON signature calculator...
#!/usr/bin/env python
# -*- coding: utf-8 -*-import base64, hmac, sha
from sys import argvscript, policy = argvprivate_key = 'uV3F3YluFJax1cknvbcGwgjvx4QpvB+leU8dUj2o'
input = open("..Desktop/policy.txt", "rb")
policy = input.read()
policy_encoded = base64.b64encode(policy)
signature = base64.b64encode(hmac.new(private_key, policy_encoded, sha).digest())
print "Your policy base-64 encoded is %s." % (policy_encoded)
print "Your signature base-64 encoded is %s." % (signature)
print "Your signature encoded should be 2qCp0odXe7A9IYyUVqn0w2adtCA="
JSON Policy (policy.txt--UTF-8)
{ "expiration": "2007-12-01T12:00:00.000Z",
"conditions": [
{"bucket": "johnsmith"},
["starts-with", "$key", "user/eric/"],
{"acl": "public-read"},
{"success_action_redirect": "http://johnsmith.s3.amazonaws.com/successful_upload.html"},
["starts-with", "$Content-Type", "image/"],
{"x-amz-meta-uuid": "14365123651274"},
["starts-with", "$x-amz-meta-tag", ""]
]
}