From 8b25ba39b8b672ba43e0b5f09000cad2332ec74e Mon Sep 17 00:00:00 2001
From: Chip Wasson <chip@wasson.io>
Date: Tue, 2 Apr 2024 16:45:09 -0600
Subject: [PATCH] Add PoW module

---
 src/app.controller.spec.ts |  2 +-
 src/app.module.ts          |  2 +
 src/pow/pow.controller.ts  | 24 +++++++++++
 src/pow/pow.module.ts      | 16 +++++++
 src/pow/pow.service.ts     | 88 ++++++++++++++++++++++++++++++++++++++
 5 files changed, 131 insertions(+), 1 deletion(-)
 create mode 100644 src/pow/pow.controller.ts
 create mode 100644 src/pow/pow.module.ts
 create mode 100644 src/pow/pow.service.ts

diff --git a/src/app.controller.spec.ts b/src/app.controller.spec.ts
index d22f389..4110be6 100644
--- a/src/app.controller.spec.ts
+++ b/src/app.controller.spec.ts
@@ -16,7 +16,7 @@ describe('AppController', () => {
 
   describe('root', () => {
     it('should return "Hello World!"', () => {
-      expect(appController.getHello()).toBe('Hello World!');
+      expect(appController.getHello()).toBe("Hello World! This is Chip's generalized API for fetching information and things. You can contact me on mastodon @chip@talking.dev.");
     });
   });
 });
diff --git a/src/app.module.ts b/src/app.module.ts
index 91f6de1..7703e1c 100644
--- a/src/app.module.ts
+++ b/src/app.module.ts
@@ -22,6 +22,7 @@ import { redisStore } from 'cache-manager-redis-yet';
 import { RedirectsModule } from './redirects/redirects.module';
 import { FileModule } from './file/file.module';
 import { FocoLiveModule } from './foco-live/foco-live.module';
+import { PowModule } from './pow/pow.module';
 
 @Module({
   imports: [
@@ -78,6 +79,7 @@ import { FocoLiveModule } from './foco-live/foco-live.module';
     RedirectsModule,
     FileModule,
     FocoLiveModule,
+    PowModule,
   ],
   controllers: [AppController],
   providers: [AppService],
diff --git a/src/pow/pow.controller.ts b/src/pow/pow.controller.ts
new file mode 100644
index 0000000..da27fbf
--- /dev/null
+++ b/src/pow/pow.controller.ts
@@ -0,0 +1,24 @@
+import { Body, Controller, Get, Post, Query } from '@nestjs/common';
+import { PowService } from './pow.service';
+import { ApiBody, ApiQuery, ApiTags } from '@nestjs/swagger';
+
+@ApiTags('pow')
+@Controller('pow')
+export class PowController {
+    constructor(
+        private readonly powService: PowService,
+    ) { }
+
+
+    @Get('challenge')
+    async generateChallenge() {
+        return this.powService.generateChallenge();
+    }
+
+    @Post('challenge')
+    @ApiBody({ schema: { properties: { challenge: { type: 'string' }, proof: { type: 'string' } } } })
+    async verifyChallenge(@Body() body: { challenge: string, proof: string }) {
+        return this.powService.verifyChallenge(body.challenge, body.proof);
+    }
+
+}
diff --git a/src/pow/pow.module.ts b/src/pow/pow.module.ts
new file mode 100644
index 0000000..6a81dbd
--- /dev/null
+++ b/src/pow/pow.module.ts
@@ -0,0 +1,16 @@
+import { Module } from '@nestjs/common';
+import { PowService } from './pow.service';
+import { CacheModule } from '@nestjs/cache-manager';
+import { PowController } from './pow.controller';
+
+@Module({
+  imports: [
+    CacheModule.register({
+      ttl: 5,
+      max: 10,
+    }),
+  ],
+  providers: [PowService],
+  controllers: [PowController]
+})
+export class PowModule { }
diff --git a/src/pow/pow.service.ts b/src/pow/pow.service.ts
new file mode 100644
index 0000000..2722930
--- /dev/null
+++ b/src/pow/pow.service.ts
@@ -0,0 +1,88 @@
+import { CACHE_MANAGER } from '@nestjs/cache-manager';
+import { Inject, Injectable, Logger } from '@nestjs/common';
+import { Cache } from 'cache-manager';
+import { randomBytes, createHash } from 'crypto';
+
+
+@Injectable()
+export class PowService {
+    private readonly logger = new Logger(PowService.name);
+    private difficulty = 5;
+
+    constructor(
+        @Inject(CACHE_MANAGER) private cacheManager: Cache,
+    ) { }
+
+    /**
+     * Generate a proof of work challenge, stored to redis for verification within
+     * the next 10 seconds.
+     */
+    async generateChallenge() {
+        const challenge = this.generateRandom256BitString();
+        console.log(challenge)
+        await this.cacheManager.set(challenge, true, 60 * 1000);
+        return challenge;
+    }
+
+    generateRandom256BitString() {
+        const randomString = randomBytes(32).toString('hex');
+        return randomString;
+    }
+
+
+    hashAndCheck(string: string) {
+        return this.hashPassesDifficulty(this.hashString(string), this.difficulty);
+    }
+
+    hashPassesDifficulty(hash: string, difficulty: number) {
+        return hash.startsWith('0'.repeat(difficulty));
+    }
+
+    /**
+     * Verify that the proof of work submitted has a leading number of
+     * zeroes equal to the challenge length and the challenge exists.
+     */
+    async verifyChallenge(challenge: string, proof: string): Promise<boolean> {
+        const expected = await this.cacheManager.get<boolean>(challenge);
+        return expected ? this.hashAndCheck(proof + challenge) : false;
+    }
+
+    async markChallengeAsComplete(challenge: string) {
+        await this.cacheManager.del(challenge);
+    }
+
+    /**
+     * Perform a proof of work challenge to find a proof that hashes to a value
+     */
+    async performChallenge(challenge: string) {
+        let proof = this.generateRandom256BitString();
+        let hash = this.hashString(proof + challenge);
+        while (!this.hashPassesDifficulty(hash, this.difficulty)) {
+            proof = this.generateRandom256BitString();
+            hash = this.hashString(proof + challenge);
+        }
+        return { proof, hash };
+    }
+
+    /**
+     * sha512 the provided string and return the result.
+     */
+    hashString(input: string) {
+        return createHash('sha512').update(input).digest('hex');
+    }
+
+    /**
+     * Set the difficulty of the proof of work challenge.
+     */
+    setDifficulty(difficulty: number) {
+        this.difficulty = difficulty;
+    }
+
+    /**
+     * Get the current difficulty of the proof of work challenge.
+     */
+    getDifficulty() {
+        return this.difficulty;
+    }
+
+}