The AWS Ruby SDK gives me a "The Content-MD5 you specified was invalid." error when I try to upload using a presigned url

Question

I'm having problems using the AWS Ruby SDK to create a pre-signed upload link to S3 while specifying an md5 hash.

md5 -q my_file.jpg
4ef248082efb309d50f1cbbbd3d7cf4a

From Rails Console:

AWS::S3.new.buckets[bucket].objects[key].url_for(:put, signature_version: :v4, content_md5: '4ef248082efb309d50f1cbbbd3d7cf4a').to_s
=> "https://s3.amazonaws.com/<rest_of_url_here>&X-Amz-SignedHeaders=Host%3BContent-MD5" 

From command line:

curl -v -H "content-md5:4ef248082efb309d50f1cbbbd3d7cf4a" -T my_file.jpg "https://s3.amazonaws.com/<rest_of_url_here>&X-Amz-SignedHeaders=Host%3BContent-MD5"

<Error><Code>InvalidDigest</Code><Message>The Content-MD5 you specified was invalid.</Message>    <RequestId>blah</RequestId><Content-MD5>4ef248082efb309d50f1cbbbd3d7cf4a</Content-MD5><HostId>blah</HostId></Error>

I can generate an upload link and upload without using content-md5. After doing that upload, I verified that the S3 object does indeed have the same MD5 hash as my local file.

Answer 1

Apparently you need the MD5 base64 encoded. Note that it's not the MD5 hex string, but the actual MD5 that needs to be encoded. I should have been using the following value:

openssl dgst -md5 -binary my_file.jpg | openssl enc -base64
TvJICC77MJ1Q8cu709fPSg==