feat: add spec to describe space/content/decrypt ability

.github/workflows/words-to-ignore.txt

@@ -175,3 +175,6 @@ InterPlanetary
 queryable
 bafy
 0-rc
+Decrypt
+decrypt
+decrypting

w3-encrypt.md

@@ -0,0 +1,161 @@
+# W3 Encrypt
+
+![wip](https://img.shields.io/badge/status-wip-orange.svg?style=flat-square)
+
+# Introduction
+
+## Abstract
+
+W3 Encrypt protocol defines a format to encrypt content and how to allow authorized agents to decrypt it. This is done through an encryption service that manages keys in a decentralized context, enabling encryption and providing a way to validate invocations for content decryption.
+
+## Concepts
+
+### Space
+
+A namespace, often referred as a "space", is an owned resource that can be shared. It corresponds to a unique asymmetric cryptographic keypair and is identified by a [`did:key`] URI.
+
+### Content
+
+A file of any type that can be encrypted and stored.
+
+### Encryption Service
+
+The encryption service performs the role of managing keys in a decentralized context. It enables encryption and provides a way to validate invocations to decrypt content. The service should implemented a secure encryption system (e.g., Lit Protocol) that supports:
+
+1. Multi-party threshold secret sharing (TSS) to enable decentralized public key cryptography
+2. Equipped with a Trusted Execution Environment (TEE)
+3. Identity-based encryption with access control conditions
+4. Secure key management
+5. UCAN validation
+
+# Capabilities
+
+## Space Content Decrypt
+
+Authorized agent MAY invoke `space/content/decrypt` capability on the [space] subject to decrypt a specified content.
+
+### Space Content Decrypt Example
+
+Invocation example illustrates Bob requesting to decrypt a content under "bafy..." in the space "did:key:zAliceSpace".
+
+```js
+{
+  "cmd": "/space/content/decrypt",
+  "sub": "did:key:zAliceSpace",
+  "iss": "did:key:zBob",
+  "aud": "did:web:storacha.netowrk",
+  "args": {
+    "resource": { "/": "bafy..." }
+  },
+  "prf": [],
+  "sig": "..."
+}
+```
+
+### Space Content Decrypt Capability
+
+#### Space Content Decrypt Capability Schema
+
+```ts
+type SpaceContentDecrypt = {
+  cmd: "/space/content/decrypt"
+  sub: SpaceDID
+  args: {
+    // Link is the Content Archive (CAR) containing the Encrypted Metadata
+    resource: Link<ContentArchive<EncryptedMetadata>>
+  }
+}
+
+// Type describes a CAR format
+type ContentArchive<T> = ByteView<{
+  roots: [Block<T>]
+  blocks: Block[]
+}>
+
+```
+
+### Encrypted Metadata
+
+#### Encrypted Metadata Schema
+
+Encrypted Metadata schema is variant type keyed by the format descriptor label designed to allow format evolution through versioning and additional schema variants.
+
+```ts
+type Index = Variant<{
+  "encrypted/metadata@0.1": EncryptedMetadata
+}>
+
+type EncryptedMetadata = {
+    encryptedDataCID: Link<any> 
+    identityBoundCiphertext: Uint8Array,
+    plaintextKeyHash: Uint8Array 
+    accessControlConditions: [Record<string, any>]
+}
+```
+
+The **Encrypted Metadata** **MUST** summarize all the necessary information required for someone with a delegation to request decryption from the encryption service for the content stored under `encryptedDataCID`.  
+
+The **Encrypted Metadata** should be generated **after** the encryption process is complete, at which point its properties can be defined as follows:
+
+| Name        | Description                                                                                                                                    |
+| ----------- | ---------------------------------------------------------------------------------------------------------------------------------------------- |
+| accessControlConditions (ACC) | Pre-determined identity parameter. |
+| plaintextKeyHash       | hash of the original data.|
+| identityBoundCiphertext    | The result of encrypting the original data and the identity parameter, which is the hash of the original data and the hash of the ACC|
+| encryptedDataCID | Represents the actual data CID of actual encrypted data.|
+
+Example:
+
+```js
+{
+  "encrypted/metadata@0.1": {
+    cypherText: new Uint8Array([109, 70, ... 61]),
+    encryptedDataCID:  { "/": "bafy..dag" },
+    dataToEncryptHash: new Uint8Array([49, 53, ... 54]),
+    accessControlConditions: [
+      {
+        chain: "ethereum",
+        method: "",
+        parameters: [
+          ":currentActionIpfsId",
+          "did:key:z6MktfnQz8Kcz5nsC65oyXWFXhbbAZQavjg6LYuHgv4YbxzN",
+        ],
+        contractAddress: "",
+        returnValueTest: {
+          value: "QmPFrQGo5RAtdSTZ4bkaeDHVGrmy2TeEUwTu4LuVAPHiMd",
+          comparator: "=",
+        },
+        standardContractType: "",
+      },
+    ],
+  },
+}
+
+```
+
+# Implementation Requirements
+
+## Encryption Service
+
+The encryption service MUST:
+
+1. Support identity-based encryption with access control conditions
+2. Provide secure decentralized key management
+3. Validate UCAN invocations for decryption
+
+## Client Implementation
+
+### Encryption
+Clients implementing this specification **MUST** use the encryption service to encrypt the key used to encrypt the content. This **double encryption strategy** is designed to better handle large files.
+
+Once the encryption key encrypted, the client **MUST** store the encrypted metadata in IPFS, encoded as **DAG-CBOR**.  
+
+### Delegation
+The client **MUST** allow users to create a delegation for decrypting the content. The delegated resource **SHOULD** be the **encrypted metadata CID**.  
+
+### Decryption
+1. The client **MUST** fetch the **encrypted metadata CAR** from IPFS to retrieve all necessary properties, including the **encryptedData** under **encryptedDataCID**.
+2. The client **MUST** authorize a session with the **Encryption Service** to call the **UCAN validation** and decryption function.
+3. **Before passing the delegation to the UCAN validation and decryption function,** the client **MUST** create an **invocation**, wrap it in a delegation, and submit it. This ensures that the function validates only the **delegation chain** and does not execute the invocation directly.
+4. The **UCAN validation and decryption function** code is stored in **IPFS** to guarantee **immutability**. This function validates the delegation chain and calls the **Encryption Service** to decrypt the key.
+5. Once the encryption key is retrieved, the client **MUST** use it to decrypt the actual content and **discard the key immediately** for security reasons.