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import { parseXml } from './parseXml'
import { sha1 } from './sha1'
export interface WechatMessageCryptoOptions {
/** 公众号/第三方平台的 APPID */
appId: string
/** 消息校验口令 */
token: string
/** 消息加解密密钥 */
encodingAESKey: string
}
export interface WechatMessageCryptoSignOptions {
/** Unix 时间戳 */
timestamp: number
/** 随机字符串 */
nonceStr: string
/** 加密后的消息 */
encryptedMsg: string
}
export interface WechatMessageCryptoSignEncryptedMsgResult {
/** Unix 时间戳 */
timestamp: number
/** 随机字符串 */
nonceStr: string
/** 签名 */
signature: string
}
/**
* 微信公众号消息加解密。
*/
export class WechatMessageCrypto {
private options!: WechatMessageCryptoOptions
private aesKey!: Buffer
private iv!: Buffer
constructor(options: WechatMessageCryptoOptions) {
this.options = options
this.aesKey = Buffer.from(`${options.encodingAESKey}=`, 'base64')
this.iv = this.aesKey.slice(0, 16)
}
/**
* 加密原始消息。
*
* @param msg 原始消息
*/
encryptMsg(msg: string): string {
const randomBytes = crypto.randomBytes(16)
const msgLenBuf = Buffer.alloc(4)
const offset = 0
msgLenBuf.writeUInt32BE(Buffer.byteLength(msg), offset)
const msgBuf = Buffer.from(msg)
const appIdBuf = Buffer.from(this.options.appId)
let totalBuf = Buffer.concat([randomBytes, msgLenBuf, msgBuf, appIdBuf])
const cipher = crypto.createCipheriv('aes-256-cbc', this.aesKey, this.iv)
cipher.setAutoPadding(false)
totalBuf = this.PKCS7Encode(totalBuf)
const encryptedBuf = Buffer.concat([
cipher.update(totalBuf),
cipher.final(),
])
return encryptedBuf.toString('base64')
}
/**
* 签名。
*
* @param options 选项
*/
sign(options: WechatMessageCryptoSignOptions): string {
return sha1(
[
this.options.token,
options.timestamp,
options.nonceStr,
options.encryptedMsg,
]
.sort((a, b) => {
a = a.toString()
b = b.toString()
return a > b ? 1 : a < b ? -1 : 0
})
.join(''),
)
}
/**
* 签名加密后的消息。
*
* @param encryptedMsg 加密后的消息
*/
signEncryptedMsg(
encryptedMsg: string,
): WechatMessageCryptoSignEncryptedMsgResult {
const timestamp = Math.round(Date.now() / 1000)
const nonceStr = timestamp.toString(36)
const signature = this.sign({ timestamp, nonceStr, encryptedMsg })
return { timestamp, nonceStr, signature }
}
/**
* 签名加密后的消息并返回封装好的 XML。
*
* @param encryptedMsg 加密后的消息
*/
signEncryptedMsgAsXml(encryptedMsg: string): string {
const { timestamp, nonceStr, signature } = this.signEncryptedMsg(
encryptedMsg,
)
return (
`<xml>` +
`<Encrypt><![CDATA[${encryptedMsg}]]></Encrypt>` +
`<MsgSignature><![CDATA[${signature}]]></MsgSignature>` +
`<TimeStamp>${timestamp}</TimeStamp>` +
`<Nonce><![CDATA[${nonceStr}]]></Nonce>` +
`</xml>`
)
}
/**
* 检查签名是否正确。
*
* @param signature 要验证的签名
* @param payload 载荷
*/
checkSignature(
signature: string,
payload: WechatMessageCryptoSignOptions,
): boolean {
return this.sign(payload) === signature
}
/**
* 解密加密后的消息。
*
* @param encryptedMsg 加密后的消息
*/
decryptEncryptedMsg(encryptedMsg: string): string {
const encryptedMsgBuf = Buffer.from(encryptedMsg, 'base64')
const decipher = crypto.createDecipheriv(
'aes-256-cbc',
this.aesKey,
this.iv,
)
decipher.setAutoPadding(false)
let decryptedBuf = Buffer.concat([
decipher.update(encryptedMsgBuf),
decipher.final(),
])
decryptedBuf = this.PKCS7Decode(decryptedBuf)
const msgSize = decryptedBuf.readUInt32BE(16)
const msgBufStartPos = 16 + 4
const msgBufEndPos = msgBufStartPos + msgSize
const msgBuf = decryptedBuf.slice(msgBufStartPos, msgBufEndPos)
return msgBuf.toString()
}
/**
* 解密加密后的消息并作为 XML 解码返回。
*
* @param encryptedMsg 加密后的消息
*/
decryptEncryptedMsgAsXml<T>(encryptedMsg: string): T {
return parseXml<{ xml: T }>(this.decryptEncryptedMsg(encryptedMsg)).xml
}
private PKCS7Decode(buf: Buffer) {
const padSize = buf[buf.length - 1]
return buf.slice(0, buf.length - padSize)
}
private PKCS7Encode(buf: Buffer) {
const padSize = 32 - (buf.length % 32)
const fillByte = padSize
const padBuf = Buffer.alloc(padSize, fillByte)
return Buffer.concat([buf, padBuf])
}
}
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