Add eth_sign documentation (#25)

source/contracts/signatures.md

@@ -11,7 +11,7 @@ All the signatures are sorted by the signer address and concatenated.
 
 ---
 ### ECDSA Signature
-`signature type > 26`
+`31 > signature type > 26`
 
 To be able to have the ECDSA signature without the need of additional data we use the signature type byte to encode `v`. 
 
@@ -20,18 +20,33 @@ To be able to have the ECDSA signature without the need of additional data we us
 
 `r`, `s` and `v` are the required parts of the ECDSA signature to recover the signer.
 
+---------
+### `eth_sign` signature
+`signature type > 30`
+
+To be able to use `eth_sign` we need to take the parameters `r`, `s` and `v` from calling `eth_sign` and set `v = v + 4`
+
+#### Constant part:
+`{32-bytes r}{32-bytes s}{1-byte v}`
+
+`r`, `s` and `v` are the required parts of the ECDSA signature to recover the signer.
+`v` will be substracted by `4` to calculate the signature.
+
 ---
 ### Contract Signature (EIP-1271)
 `signature type == 0`
 
 #### Constant part:
-`{32-bytes signature verifier}{32-bytes data position}`
+`{32-bytes signature verifier}{32-bytes data position}{1-byte signature type}`
 
 **Signature verifier** - Padded address of the contract that implements the EIP 1271 interface to verify the signature
+
 **Data position** - Position of the start of the signature data (offset relative to the beginning of the signature data)
 
-#### Dynamic part:
-`{bytes signature data}`
+**Signature type** - 0
+
+#### Dynamic part (solidity `bytes`):
+`{32-bytes signature length}{bytes signature data}`
 
 **Signature data** - Signature bytes that are verified by the signature verifier
 
@@ -42,10 +57,11 @@ The method `signMessage` can be used to mark a message as signed on-chain.
 `signature type == 1`
 
 #### Constant Part:
-`{32-bytes hash validator}`
+`{32-bytes hash validator}{32-bytes ignored}{1-byte signature type}`
 
 **Hash validator** - Padded address of the account that pre-validated the hash that should be validated. The Safe keeps track of all hashes that have been pre validated. This is done with a **mapping address to mapping of bytes32 to boolean** where it is possible to set a hash as validated by a certain address (hash validator). To add an entry to this mapping use `approveHash`. Also if the validator is the sender of transaction that executed the Safe transaction it is **not** required to use `approveHash` to add an entry to the mapping. (This can be seen in the [Team Edition tests](https://github.com/gnosis/safe-contracts/blob/v1.0.0/test/gnosisSafeTeamEdition.js))
 
+**Signature type** - 1
 
 
 ## Examples
@@ -68,3 +84,4 @@ The signatures bytes used for `execTransaction` would therefore be the following
 "bde0b9f486b1960454e326375d0b1680243e031fd4fb3f070d9a3ef9871ccfd57d1a653cffb6321f889169f08e548684e005f2b0c3a6c06fba4c4a68f5e006241c" + // encoded ECDSA signature
 "000000000000000000000000000000000000000000000000000000000000000800000000000000000000000000000000000000000000000000000000deadbeef"     // length of bytes + data of bytes
 ```
+