Java RSA 加密方法实现 - 使用公钥加密字符串

The given code is a method implementation in Java that performs RSA encryption using a public key. Here's a breakdown of the code:
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1. The method is declared with the signature `public static String RSAencrypt(String str, String publicKey)`. It takes two parameters - the string to be encrypted (`str`) and the public key used for encryption (`publicKey`).\n\
2. The public key is expected to be in base64 encoding. The code decodes the base64 string into a byte array using `BASE64Decoder()` from the `sun.misc` package.
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3. The decoded byte array is then used to create an `X509EncodedKeySpec` object. This object represents the key specification used to generate a public key.
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4. The `KeyFactory.getInstance("RSA")` method is used to obtain an instance of the RSA key factory.
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5. The `generatePublic(x509Key)` method is called on the RSA key factory to generate a `RSAPublicKey` object from the `X509EncodedKeySpec`.
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6. Next, a `Cipher` object is created using `Cipher.getInstance("RSA")`. The `Cipher` class provides the functionality of a cryptographic cipher for encryption and decryption.
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7. The cipher is initialized for encryption mode using `cipher.init(Cipher.ENCRYPT_MODE, pubKey)`, where `pubKey` is the `RSAPublicKey` obtained earlier.
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8. Finally, the `cipher.doFinal(str.getBytes("UTF-8"))` method is used to encrypt the input string `str` and return the result as a byte array. The result is then encoded in base64 using `BASE64Encoder()` from the `sun.misc` package and returned as a string.
   
   Note: The code uses deprecated classes from the `sun.misc` package (`BASE64Decoder` and `BASE64Encoder`). It is recommended to use a third-party library like Apache Commons Codec or Java 8's `java.util.Base64` for base64 encoding and decoding.