feat(server): improve crypto (#13822)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Bug Fixes**
  * Resolved cryptographic compatibility issues with OpenSSL 3.x.

* **New Features**
  * Broader support for multiple key types for signing and verification.
  * OTP generation adjusted (affects digit distribution/values).

* **Refactor**
* Internal cryptographic key handling reworked for improved stability,
compatibility, and multi-key-type support.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/base/helpers/crypto.ts

@@ -2,13 +2,17 @@ import {
   createCipheriv,
   createDecipheriv,
   createHash,
+  createPrivateKey,
   createPublicKey,
   createSign,
   createVerify,
   generateKeyPairSync,
+  type KeyObject,
   randomBytes,
   randomInt,
+  sign,
   timingSafeEqual,
+  verify,
 } from 'node:crypto';
 
 import { Injectable, Logger, OnModuleInit } from '@nestjs/common';
@@ -32,20 +36,31 @@ function generatePrivateKey(): string {
     namedCurve: 'prime256v1',
   });
 
+  // Export EC private key as PKCS#8 PEM. This avoids OpenSSL 3.x decoder issues
+  // in Node.js 22 when later deriving the public key via createPublicKey.
   const key = privateKey.export({
-    type: 'sec1',
+    type: 'pkcs8',
     format: 'pem',
   });
 
   return key.toString('utf8');
 }
 
-function generatePublicKey(privateKey: string) {
-  return createPublicKey({
-    key: Buffer.from(privateKey),
-  })
-    .export({ format: 'pem', type: 'spki' })
-    .toString('utf8');
+function parseKey(privateKey: string) {
+  const keyBuf = Buffer.from(privateKey);
+  let priv: KeyObject;
+  try {
+    priv = createPrivateKey({ key: keyBuf, format: 'pem', type: 'pkcs8' });
+  } catch (e1) {
+    try {
+      priv = createPrivateKey({ key: keyBuf, format: 'pem', type: 'sec1' });
+    } catch (e2) {
+      // As a last resort rely on auto-detection
+      priv = createPrivateKey(keyBuf);
+    }
+  }
+  const pub = createPublicKey(priv);
+  return { priv, pub };
 }
 
 @Injectable()
@@ -53,8 +68,8 @@ export class CryptoHelper implements OnModuleInit {
   logger = new Logger(CryptoHelper.name);
 
   keyPair!: {
-    publicKey: Buffer;
-    privateKey: Buffer;
+    publicKey: KeyObject;
+    privateKey: KeyObject;
     sha256: {
       publicKey: Buffer;
       privateKey: Buffer;
@@ -87,11 +102,14 @@ export class CryptoHelper implements OnModuleInit {
 
   private setup() {
     const privateKey = this.config.crypto.privateKey || generatePrivateKey();
-    const publicKey = generatePublicKey(privateKey);
+    const { priv, pub } = parseKey(privateKey);
+    const publicKey = pub
+      .export({ format: 'pem', type: 'spki' })
+      .toString('utf8');
 
     this.keyPair = {
-      publicKey: Buffer.from(publicKey),
-      privateKey: Buffer.from(privateKey),
+      publicKey: pub,
+      privateKey: priv,
       sha256: {
         publicKey: this.sha256(publicKey),
         privateKey: this.sha256(privateKey),
@@ -99,11 +117,23 @@ export class CryptoHelper implements OnModuleInit {
     };
   }
 
+  private get keyType() {
+    return (this.keyPair.privateKey.asymmetricKeyType as string) || 'ec';
+  }
+
   sign(data: string) {
-    const sign = createSign('rsa-sha256');
-    sign.update(data, 'utf-8');
-    sign.end();
-    return `${data},${sign.sign(this.keyPair.privateKey, 'base64')}`;
+    const input = Buffer.from(data, 'utf-8');
+    if (this.keyType === 'ed25519') {
+      // Ed25519 signs the message directly (no pre-hash)
+      const sig = sign(null, input, this.keyPair.privateKey);
+      return `${data},${sig.toString('base64')}`;
+    } else {
+      // ECDSA with SHA-256 for EC keys
+      const sign = createSign('sha256');
+      sign.update(input);
+      sign.end();
+      return `${data},${sign.sign(this.keyPair.privateKey, 'base64')}`;
+    }
   }
 
   verify(signatureWithData: string) {
@@ -111,10 +141,18 @@ export class CryptoHelper implements OnModuleInit {
     if (!signature) {
       return false;
     }
-    const verify = createVerify('rsa-sha256');
-    verify.update(data, 'utf-8');
-    verify.end();
-    return verify.verify(this.keyPair.privateKey, signature, 'base64');
+    const input = Buffer.from(data, 'utf-8');
+    const sigBuf = Buffer.from(signature, 'base64');
+    if (this.keyType === 'ed25519') {
+      // Ed25519 verifies the message directly
+      return verify(null, input, this.keyPair.publicKey, sigBuf);
+    } else {
+      // ECDSA with SHA-256
+      const verify = createVerify('sha256');
+      verify.update(input);
+      verify.end();
+      return verify.verify(this.keyPair.publicKey, sigBuf);
+    }
   }
 
   encrypt(data: string) {
@@ -179,7 +217,7 @@ export class CryptoHelper implements OnModuleInit {
     let otp = '';
 
     for (let i = 0; i < length; i++) {
-      otp += this.randomInt(0, 9).toString();
+      otp += this.randomInt(0, 10).toString();
     }
 
     return otp;