通過證書拿到公鑰，進行加密、解密

InputStream is = this.getAssets().open(fileName);//證書讀取流

CertificateFactory cf = CertificateFactory.getInstance("X.509");//獲取X.509的證書工廠

X509Certificate certificate = (X509Certificate) cf.generateCertificate(is);//獲取證書實例

PublicKey publicKey = certificate.getPublicKey();//獲取證書公鑰

Cipher tcsCipher = Cipher.getInstance(publicKey.getAlgorithm());//通過公鑰的加密算法獲取加解密實例

　　　　tcsCipher.init(Cipher.ENCRYPT_MODE, publicKey);//通過公鑰初始化實例

byte[] encode = Base64.encode("123".getBytes(),Base64.DEFAULT);/* 要加密的字符串進行編碼 */

byte[] doFinal = tcsCipher.doFinal(encode);/*加密*/

String tcsEncryptPassword = Base64.encodeToString(doFinal, Base64.DEFAULT);/* 將加密后的字符串進行編碼 */