Uploading Photos signature

i'm trying upload photos by following documentaton (http://
www.flickr.com/services/api/upload.api.html)
and get "Invalid signature".

source string for signature: 
MYSECRETapi_keyMYAPIKEYauth_tokenMYAUTHTOKENdescriptionSOMEDESCR

what is correct signature?




 
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