Switched from HMAC-SHA1 to HMAC-SHA256 signature

While both are supported by AWS, the latter is stronger hash function.
It is not believed to contain some security flaws identified in SHA-1.
So sayeth Wikipedia - http://en.wikipedia.org/wiki/SHA-2

Ubuntu Enterprise Cloud (Eucalyptus) doesn't seem to allow requests
using HMAC-SHA1. This is one of the changes I had to make to get
amazon-ec2 gem working against my Eucalyptus cluster.

lib/AWS.rb

@@ -87,7 +87,7 @@ def AWS.canonical_string(params, host, method="POST", base="/")
   # @param [Boolean] urlencode whether or not to url encode the result., true or false
   # @return [String] the signed and encoded string.
   def AWS.encode(secret_access_key, str, urlencode=true)
-    digest = OpenSSL::Digest::Digest.new('sha1')
+    digest = OpenSSL::Digest::Digest.new('sha256')
     b64_hmac =
       Base64.encode64(
         OpenSSL::HMAC.digest(digest, secret_access_key, str)).gsub("\n","")
@@ -231,7 +231,7 @@ def make_request(action, params, data='')
 
           params.merge!( {"Action" => action,
                           "SignatureVersion" => "2",
-                          "SignatureMethod" => 'HmacSHA1',
+                          "SignatureMethod" => 'HmacSHA256',
                           "AWSAccessKeyId" => @access_key_id,
                           "Version" => api_version,
                           "Timestamp"=>Time.now.getutc.iso8601} )

test/test_EC2.rb

@@ -61,8 +61,8 @@
   end
 
   specify "AWS.encode should return the expected string" do
-    AWS.encode("secretaccesskey", "foobar123", urlencode=true).should.equal "e3jeuDc3DIX2mW8cVqWiByj4j5g%3D"
-    AWS.encode("secretaccesskey", "foobar123", urlencode=false).should.equal "e3jeuDc3DIX2mW8cVqWiByj4j5g="
+    AWS.encode("secretaccesskey", "foobar123", urlencode=true).should.equal "CPzGGhtvlG3P3yp88fPZp0HKouUV8mQK1ZcdFGQeAug%3D"
+    AWS.encode("secretaccesskey", "foobar123", urlencode=false).should.equal "CPzGGhtvlG3P3yp88fPZp0HKouUV8mQK1ZcdFGQeAug="
   end
 
 end