Add Identity Visual Representation

docs/spec/2-account.md

@@ -48,6 +48,9 @@ This specification explains what Status account is, and how a node establishes t
   - [De/Serialization Process Flow](#deserialization-process-flow)
     - [Serialization Example](#serialization-example)
     - [Deserialization Example](#deserialization-example)
+- [Identity Visual Representation](#visual-identity-representation)
+  - [Emoji Hash](#emoji-hash)
+  - [Identicon Ring](#identicon-ring)
 - [Security Considerations](#security-considerations)
 - [Changelog](#changelog)
   - [Version 0.3](#version-03)
@@ -416,6 +419,68 @@ For the user, the deserialization process is exactly the same as serialization w
 
 For further guidance on the implementation of public key de/serialization consult the [`status-go` implementation and tests](https://github.com/status-im/status-go/blob/c9772325f2dca76b3504191c53313663ca2efbe5/api/utils_test.go).  
 
+## Identity Visual Representation
+Identity Visual Representation is a mechanism to minimize the risk of impersonation attacks. It is composed of two elements (Emoji Hash and Color Hash) that together deterministically reflect the [User's Chat Public Key](#publicprivate-keypairs). The client app MAY use it as an enhancement to profile/identity representation in the user interface.
+
+Each of the two components MUST encode corresponding parts of the Compressed Chat Public Key.
+
+Comporessed secp256k1 pk:
+|prefix       |x coord   |
+|-------------|----------|
+|0x02 or 0x03 | 32 bytes |
+
+```text
+0x03 (prefix)
+086138b210f21d41c757ae8a5d2a4cb29c1350f7389517608378ebd9efcf4a55 (x coord)
+```
+
+Identity Visual Representation mapping:
+|Emoji Hash|Color Hash|
+|----------|----------|
+|0x02 or 0x03 + 16 bytes (first half of x coord) | 16 bytes (second half of x coord) |
+
+```text
+03086138b210f21d41c757ae8a5d2a4cb2 (17 bytes encoded as Emoji Hash)
+9c1350f7389517608378ebd9efcf4a55 (16 bytes encoded as Color Hash)
+```
+
+### Emoji Hash
+Emoji Hash is a deterministic sequence of emojis that (in conjunction with Color Hash) uniquely identifies a profile. It encodes the first 17 bytes of data from the Compressed Chat Public Key.
+
+- Emoji Hash MUST be a sequence of `len` distinctive emojis
+- Emoji Hash MUST be one of `n` distinctive emojis
+- emojis set of length `n` used for Emoji Hash MUST be immutable
+
+Emoji Hash to be collision resistant MUST fulfill given equasion: $\frac{n!}{(n-len)!} \geq 2^{(17*8)}$
+
+Sample values:
+|len|n       |
+|---|--------|
+|12 | >= 2586|
+|14 | >= 847 |
+|16 | >= 264 |
+
+### Color Hash
+Color Hash is a deterministic sequence of colors that (in conjunction with Emoji Hash) uniquely identifies a profile. It encodes the last 16 bytes of data from the Compressed Chat Public Key.
+
+- Color Hash MUST be exactly `u` units length (unit represents physical entity with color assigned, e.g. pixel)
+- Color Hash unit MUST be one of `c` distinctive colors
+- `c` distictive colors set used for Color Hash MUST be immutable
+- Color Hash MUST be composed of `s` color segments
+- Color Hash segment MUST be composed by units of the same color
+- Color Hash segment MAY be of different length
+- Color Hash MUST NOT contain same color segments
+
+Color Hash to be collision resistant MUST fulfill given equastion: $\frac{(u-1)!}{(s-1)!(u-s)!} \times \frac{c!}{(c-s)!} \geq 2^{(16*8)}$
+
+Sample values:
+|u   |s   |c      |
+|----|----|-------|
+|64  | 12 | >= 175|
+|64  | 16 | >= 42 |
+|128 | 14 | >= 40 |
+|256 | 12 | >= 50 |
+
 ## Security Considerations
 
 -