Another amazon example, this time based on StackOverflow question that gets it right, and showing that amazon is wrong

amazon-signing-debug2.py

# first example and code taken from:
# http://stackoverflow.com/questions/9018767/python-generated-signature-for-s3-post
# second set of data taken from amazon official examples
import base64, hmac, sha

private_key = 'uV3F3YluFJax1cknvbcGwgjvx4QpvB+leU8dUj2o'
#input = open("policy.txt", "rb")
#policy = input.read()
policy_encoded = "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"
expected = "2qCp0odXe7A9IYyUVqn0w2adtCA="
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 %s." % (expected,)
            
private_key = "wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY"
policy_encoded = "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"
signature = base64.b64encode(hmac.new(private_key, policy_encoded, sha).digest())
expected = "qA7FWXKq6VvU68lI9KdveT1cWgF="
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 %s." % (expected,)