From 55569c55235c0a82525b142ea9a4f8a2669654ce Mon Sep 17 00:00:00 2001
From: haotianlong <haotianlong@tencent.com>
Date: Tue, 9 Jul 2024 15:14:34 +0800
Subject: [PATCH] fix(asn1): correct the implementation of the long version of
 L encoding in asn.1

---
 src/sm2/asn1.ts  |  8 +++++++-
 test/sm2.test.ts | 25 +++++++++++++++++++++++--
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/src/sm2/asn1.ts b/src/sm2/asn1.ts
index 9fedc19..e2534d3 100755
--- a/src/sm2/asn1.ts
+++ b/src/sm2/asn1.ts
@@ -113,7 +113,13 @@ class DERSequence extends ASN1Object {
  */
 function getLenOfL(str: string, start: number) {
   if (+str[start + 2] < 8) return 1 // l 以0开头，则表示短格式，只占一个字节
-  return +str.substring(start + 2, start + 4) & 0x7f + 1 // 长格式，取第一个字节后7位作为长度真正占用字节数，再加上本身
+  // 长格式，取第一个字节后7位作为长度真正占用字节数，再加上本身
+  const encoded = str.slice(start + 2, start + 6);
+  const headHex = encoded.slice(0, 2);
+  const head = parseInt(headHex, 16);
+  const nHexLength = (head - 128) * 2;
+
+  return nHexLength;
 }
 
 /**
diff --git a/test/sm2.test.ts b/test/sm2.test.ts
index ddf17a1..c0170c5 100644
--- a/test/sm2.test.ts
+++ b/test/sm2.test.ts
@@ -96,17 +96,38 @@ describe('sm2: encrypt and decrypt data', () => {
 
 
 describe('sm2: encrypt and decrypt data using asn1 encoding', () => {
-    it('decrypted data should be correct', () => {
+    it('decrypted data should be correct (non asn.1)', () => {
         const input = 'aabbccdd'
         const res = sm2.doEncrypt(hexToArray(input), '049812a275eca335e85998eb4030a6cc9e88a098010bdbfc134b26e29c43253439d3821ef18e69e0813bcc55eee7dc9163f1edb81ad2032b20cbdf1408897faaac', 1, {
-            asn1: true,
+            asn1: false,
         })
         // console.log('res', res)
+        const dec = sm2.doDecrypt(res, '75b25a5d6101013e9be25816f81cf1f64bf78ea8383b32d61f5b26e6f1429e70', 1, {
+            output: 'array',
+            asn1: false,
+        })
+        expect(arrayToHex([...dec])).toBe(input)
+    })
+    it('decrypted data should be correct (asn.1)', () => {
+        const input = 'aabbccdd'
+        const res = sm2.doEncrypt(hexToArray(input), '049812a275eca335e85998eb4030a6cc9e88a098010bdbfc134b26e29c43253439d3821ef18e69e0813bcc55eee7dc9163f1edb81ad2032b20cbdf1408897faaac', 1, {
+            asn1: true,
+        })
         const dec = sm2.doDecrypt(res, '75b25a5d6101013e9be25816f81cf1f64bf78ea8383b32d61f5b26e6f1429e70', 1, {
             output: 'array',
             asn1: true,
         })
         expect(arrayToHex([...dec])).toBe(input)
+        const input2 = 'xxxxx{"xx": "111","t": "1"}'
+        const res2 = sm2.doEncrypt(input2, '049812a275eca335e85998eb4030a6cc9e88a098010bdbfc134b26e29c43253439d3821ef18e69e0813bcc55eee7dc9163f1edb81ad2032b20cbdf1408897faaac', 1, {
+            asn1: true,
+        })
+        console.log(res2)
+        const dec2 = sm2.doDecrypt(res2, '75b25a5d6101013e9be25816f81cf1f64bf78ea8383b32d61f5b26e6f1429e70', 1, {
+            output: 'string',
+            asn1: true,
+        })
+        expect(dec2).toBe(input2)
     })
     it('decrypted data should be correct: c1c2c3', () => {
         const input = 'aabbccdd'