{"action":"created","comment":{"url":"https://api.github.com/repos/NebulousLabs/Sia/pulls/comments/54332886","id":54332886,"diff_hunk":"@@ -69,8 +71,35 @@ func VerifyHash(data Hash, pk PublicKey, sig Signature) error {\n \treturn nil\n }\n \n+// WriteSignedData writes a length-prefixed object followed by its signature.\n+func WriteSignedData(w io.Writer, obj interface{}, sk SecretKey) error {\n+\tb := encoding.Marshal(obj)\n+\tsig, _ := SignHash(HashBytes(b), sk) // no error possible\n+\treturn encoding.NewEncoder(w).EncodeAll(b, sig)\n+}\n+\n+// ReadSignedData reads a length-prefixed object followed by its signature,\n+// and verifies the signature.\n+func ReadSignedData(r io.Reader, obj interface{}, maxLen uint64, pk PublicKey) error {\n+\t// read the encoded data and signature\n+\tdata, err := encoding.ReadPrefix(r, maxLen)\n+\tif err != nil {\n+\t\treturn err\n+\t}\n+\tvar sig Signature\n+\tif err := encoding.NewDecoder(r).Decode(&sig); err != nil {\n+\t\treturn err\n+\t}\n+\t// verify the signature\n+\tif err := VerifyHash(HashBytes(data), pk, sig); err != nil {\n+\t\treturn err\n+\t}\n+\t// decode the object\n+\treturn encoding.Unmarshal(data, obj)\n+}","path":"crypto/signatures.go","position":57,"original_position":57,"commit_id":"b51f2c681305d3c2b56290765ba22385d52df171","original_commit_id":"b51f2c681305d3c2b56290765ba22385d52df171","user":{"login":"DavidVorick","id":2316841,"avatar_url":"https://avatars.githubusercontent.com/u/2316841?v=3","gravatar_id":"","url":"https://api.github.com/users/DavidVorick","html_url":"https://github.com/DavidVorick","followers_url":"https://api.github.com/users/DavidVorick/followers","following_url":"https://api.github.com/users/DavidVorick/following{/other_user}","gists_url":"https://api.github.com/users/DavidVorick/gists{/gist_id}","starred_url":"https://api.github.com/users/DavidVorick/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/DavidVorick/subscriptions","organizations_url":"https://api.github.com/users/DavidVorick/orgs","repos_url":"https://api.github.com/users/DavidVorick/repos","events_url":"https://api.github.com/users/DavidVorick/events{/privacy}","received_events_url":"https://api.github.com/users/DavidVorick/received_events","type":"User","site_admin":false},"body":"similarly, I find it confusing that this is a reader.","created_at":"2016-02-27T12:41:01Z","updated_at":"2016-02-27T12:41:01Z","html_url":"https://github.com/NebulousLabs/Sia/pull/997#discussion_r54332886","pull_request_url":"https://api.github.com/repos/NebulousLabs/Sia/pulls/997","_links":{"self":{"href":"https://api.github.com/repos/NebulousLabs/Sia/pulls/comments/54332886"},"html":{"href":"https://github.com/NebulousLabs/Sia/pull/997#discussion_r54332886"},"pull_request":{"href":"https://api.github.com/repos/NebulousLabs/Sia/pulls/997"}}},"pull_request":{"url":"https://api.github.com/repos/NebulousLabs/Sia/pulls/997","id":60939989,"html_url":"https://github.com/NebulousLabs/Sia/pull/997","diff_url":"https://github.com/NebulousLabs/Sia/pull/997.diff","patch_url":"https://github.com/NebulousLabs/Sia/pull/997.patch","issue_url":"https://api.github.com/repos/NebulousLabs/Sia/issues/997","number":997,"state":"open","locked":false,"title":"Object signing helpers","user":{"login":"lukechampine","id":3344749,"avatar_url":"https://avatars.githubusercontent.com/u/3344749?v=3","gravatar_id":"","url":"https://api.github.com/users/lukechampine","html_url":"https://github.com/lukechampine","followers_url":"https://api.github.com/users/lukechampine/followers","following_url":"https://api.github.com/users/lukechampine/following{/other_user}","gists_url":"https://api.github.com/users/lukechampine/gists{/gist_id}","starred_url":"https://api.github.com/users/lukechampine/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/lukechampine/subscriptions","organizations_url":"https://api.github.com/users/lukechampine/orgs","repos_url":"https://api.github.com/users/lukechampine/repos","events_url":"https://api.github.com/users/lukechampine/events{/privacy}","received_events_url":"https://api.github.com/users/lukechampine/received_events","type":"User","site_admin":false},"body":"Add two functions to the crypto package: `WriteSignedObject` and `ReadSignedObject`. They function identicially to `encoding.WriteObject` and `encoding.ReadObject`, except that `WriteSignedObject` also writes a signature of the encoded object's hash, and `ReadSignedObject` reads and verifies that hash. These functions will be useful in the new host/renter protocol, which requires reading and writing signed data. Both have 100% code coverage.\r\n(Question: could we sign the object directly, instead of its hash?)\r\n\r\nThere is one quirk to the implementation, which is that the signature is not included in the length prefix. Most objects sent over a network carry a length-prefix, so that the receiver knows how much data to expect. Since the signature size is constant, we can remove its length prefix, saving 8 bytes.\r\n\r\nAlso add proper testing of the `PublicKey` 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