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POPython Generated Signature for S3 Post
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copied!<p>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:</p> <p><a href="http://doc.s3.amazonaws.com/proposals/post.html" rel="noreferrer">http://doc.s3.amazonaws.com/proposals/post.html</a></p> <p>And even found this:</p> <p><a href="http://s3.amazonaws.com/doc/s3-example-code/post/post_sample.html" rel="noreferrer">http://s3.amazonaws.com/doc/s3-example-code/post/post_sample.html</a></p> <p>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. </p> <p>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?</p> <p>The script I'm working with is below, the policy and the AWS Secret Key <code>private_key</code> 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.</p> <p>Can anyone tell me why the signature as calculated below does not match the reference signature provided by Amazon?:</p> <p>In other words: </p> <p>Why this is correctly encoded:</p> <pre><code>policy_encoded = base64.b64encode(policy) </code></pre> <p>but this one is NOT:</p> <pre><code>signature = base64.b64encode(hmac.new(private_key, policy_encoded, sha).digest()) </code></pre> <p>PYTHON signature calculator...</p> <pre><code>#!/usr/bin/env python # -*- coding: utf-8 -*- import base64, hmac, sha from sys import argv script, policy = argv private_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=" </code></pre> <p>JSON Policy (policy.txt--UTF-8)</p> <pre><code>{ "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", ""] ] } </code></pre>

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