Inconsistent SignatureDoesNotMatch Amazon S3 with

Question

I have 2 files compiled by django-pipeline along with s3boto: master.css and master.js. They are set to "Public" in my buckets. However, when I access them, sometimes master.css is served, sometimes it errs with SignatureDoesNotMatch. The same with master.js. This doesn't happen on Chrome. What could I be missing?

EDIT: It now happens on Chrome too.

Answer 1

Happened to me too... Took a few hours to find, but I figured it out eventually. Turns out that if the right signature is :

ssCNsAOxLf5vA80ldAI3M0CU2%2Bw=

Then AWS will NOT accept:

ssCNsAOxLf5vA80ldAI3M0CU2+w=

Where the only difference is the translation of %2B to '+'.

S3BotoStorage actually yields it correctly but the encoding happens on CachedFilesMixin in the final line of the url method (return unquote(final_url)). To fix it, I derived a new CachedFilesMixin to undo the "damage" (I should mention that I don't know why this unquote exists in the first place, so undoing it might cause other problems)

class MyCachedFilesMixin(CachedFilesMixin):
def url(self, *a, **kw):
    s = super(MyCachedFilesMixin, self).url(*a, **kw)
    if isinstance(s, unicode):
        s = s.encode('utf-8', 'ignore')
    scheme, netloc, path, qs, anchor = urlparse.urlsplit(s)
    path = urllib.quote(path, '/%')
    qs = urllib.quote_plus(qs, ':&=')
    return urlparse.urlunsplit((scheme, netloc, path, qs, anchor))

Where I used the code I found here.

Hope this helps...

Answer 2

This article on Flask is a good resource on getting your signatures right: https://devcenter.heroku.com/articles/s3-upload-python

@app.route('/sign_s3/')
def sign_s3():
    AWS_ACCESS_KEY = os.environ.get('AWS_ACCESS_KEY_ID')       
    AWS_SECRET_KEY = os.environ.get('AWS_SECRET_ACCESS_KEY')
    S3_BUCKET = os.environ.get('S3_BUCKET')

    object_name = request.args.get('s3_object_name')
    mime_type = request.args.get('s3_object_type')

    expires = int(time.time()+10)
    amz_headers = "x-amz-acl:public-read"

    put_request = "PUT\n\n%s\n%d\n%s\n/%s/%s" % (mime_type, expires, amz_headers, S3_BUCKET, object_name)

    signature = base64.encodestring(hmac.new(AWS_SECRET_KEY,put_request, sha).digest())
    signature = urllib.quote_plus(signature.strip())

    url = 'https://%s.s3.amazonaws.com/%s' % (S3_BUCKET, object_name)

    return json.dumps({
        'signed_request': '%s?AWSAccessKeyId=%s&Expires=%d&Signature=%s' % (url, AWS_ACCESS_KEY, expires, signature),
         'url': url
    })

Answer 3

I was struggling with this for a while, and I didn't like the idea of messing up with CachedFilesMixin (seemed like an overkill to me).

Until a proper fix is issued to the django platform, I've found quoting the signature two times is a good option. I know it's not pretty, but it works and it's simple.

So you'll just have to do something like this:

signature = urllib.quote_plus(signature.strip())
signature = urllib.quote_plus(signature.strip())

Hope it helps!

Answer 4

I had a similar issue causing SignatureDoesNotMatch errors when downloading files using an S3 signed URL and the python requests HTTP library.

My problem ended up being a bad content-type. The documentation at AWS on Authenticating REST Requests helped me figure it out, and has examples in Python.