add ali captcha

pkg/captcha/encrypt_scene.go

@@ -0,0 +1,61 @@
+package captcha
+
+import (
+	"bytes"
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+	"io"
+	"time"
+)
+
+// GenerateEncryptedSceneID 按阿里云文档生成 EncryptedSceneId（仅适用于 V3 架构加密模式）。
+// 明文格式: sceneId&timestamp&expireTime
+// 加密: AES-256-CBC + PKCS7Padding，结果为 Base64( IV(16字节) + ciphertext )
+func GenerateEncryptedSceneID(sceneId, ekey string, expireSeconds int) (string, error) {
+	if expireSeconds <= 0 || expireSeconds > 86400 {
+		expireSeconds = 3600
+	}
+
+	ts := time.Now().Unix() // 秒级时间戳
+	plaintext := fmt.Sprintf("%s&%d&%d", sceneId, ts, expireSeconds)
+
+	keyBytes, err := base64.StdEncoding.DecodeString(ekey)
+	if err != nil {
+		return "", fmt.Errorf("decode ekey error: %w", err)
+	}
+	if len(keyBytes) != 32 {
+		return "", fmt.Errorf("invalid ekey length, need 32 bytes after base64 decode, got %d", len(keyBytes))
+	}
+
+	block, err := aes.NewCipher(keyBytes)
+	if err != nil {
+		return "", fmt.Errorf("new cipher error: %w", err)
+	}
+
+	iv := make([]byte, aes.BlockSize)
+	if _, err := io.ReadFull(rand.Reader, iv); err != nil {
+		return "", fmt.Errorf("read iv error: %w", err)
+	}
+
+	padded := pkcs7Pad([]byte(plaintext), aes.BlockSize)
+	ciphertext := make([]byte, len(padded))
+
+	mode := cipher.NewCBCEncrypter(block, iv)
+	mode.CryptBlocks(ciphertext, padded)
+
+	out := append(iv, ciphertext...)
+	return base64.StdEncoding.EncodeToString(out), nil
+}
+
+func pkcs7Pad(src []byte, blockSize int) []byte {
+	padLen := blockSize - len(src)%blockSize
+	if padLen == 0 {
+		padLen = blockSize
+	}
+	pad := bytes.Repeat([]byte{byte(padLen)}, padLen)
+	return append(src, pad...)
+}
+