add signature function (#82)

src/index.ts

@@ -1,2 +1,3 @@
 export { AES256Encryption } from './aes256-encryption';
 export { RSAEncryption } from './rsa-encryption';
+export { Signature } from './signature';

src/signature.ts

@@ -0,0 +1,23 @@
+import { createHash } from 'crypto';
+import { Encoding, SignAlgorithm } from './types';
+
+export class Signature {
+  private algorithm: SignAlgorithm;
+  private encoding: Encoding;
+  constructor(algorithm: SignAlgorithm, encoding?: Encoding) {
+    this.algorithm = algorithm;
+    this.encoding = encoding ? encoding : 'base64';
+  }
+
+  generate(data: string) {
+    const hash = createHash(this.algorithm);
+    hash.update(data);
+    const createSignature = hash.digest().toString(this.encoding);
+    return createSignature;
+  }
+
+  verify(data: string, signature: string) {
+    const createSignature = this.generate(data);
+    return createSignature === signature;
+  }
+}

src/types/encoding.ts

@@ -0,0 +1 @@
+export type Encoding = 'base64' | 'hex';

src/types/index.ts

@@ -1,2 +1,4 @@
 export * from './bit-length';
 export * from './cipher-aes256-mode';
+export * from './encoding';
+export * from './sign-algorithm';

src/types/sign-algorithm.ts

@@ -0,0 +1 @@
+export type SignAlgorithm = 'SHA1';

test/Signature.test.ts

@@ -0,0 +1,3 @@
+import {Signature} from '../src'
+test('verify signature', () => {
+});