Comment 38 for bug 1278529

I had the same BackendException on Debian wheezy with duplicity 0.6.24-1~bpo70 and python-boto 2.25.0-1~bpo7. I solved this for me by forcing boto to use "Signature Version 4" for API requests. Export this variable into the shell environment before running duply:

export S3_USE_SIGV4="True"
duply ...

According to the AWS documentation [1], new regions introduced after January 2014 do not support older signature versions in API requests. In my case, the endpoint I use is Frankfurt, EU which was introduced after this date. This version of boto supports the new signatures, but does not seem to use them without being told to do so.

Also make sure you use the hostname for your region in the URL such as s3://s3-eu-central-1.amazonaws.com/<bucket>/. I hope this helps anyone stumbling across this bug report even if it is already fixed in duplicity >= 0.7.01 as stated above.

[1] http://docs.aws.amazon.com/AmazonS3/latest/API/sig-v4-authenticating-requests.html