RSA關於加密長度限制的解決辦法
因為rsa采用分塊進行加密的,所以有長度限制.如果加密信息較多,可分段加解密(不建議對大量信息rsa加密,效率低效):
正常加密情形如下:
public
static
String encrypt(String
source
, String
publicKey
)
throws
Exception {
Key
key
= getPublicKey(
publicKey
);
/** 得到Cipher對象來實現對源數據的RSA加密 */
Cipher
cipher
= Cipher.getInstance(
"RSA/ECB/PKCS1Padding"
);
cipher
.init(Cipher.
ENCRYPT_MODE
,
key
);
byte
[]
b
=
source
.getBytes();
/** 執行加密操作 */
byte
[]
b1
=
cipher
.doFinal(
b
);
return
new
String(Base64. encodeBase64(
b1
),
"UTF-8"
);
}
分段加密如下:
public
static
byte
[] encryptByPublicKey(
byte
[]
data
, String
publicKeyStr
)
throws
Exception
{
PublicKey
publicKey
= RSAEncrypt.loadPublicKeyByStr(
publicKeyStr
);
Cipher
cipher
=
null
;
// 使用默認RSA
cipher
= Cipher.getInstance(
"RSA"
);
cipher
.init(Cipher.
ENCRYPT_MODE
,
publicKey
);
int
inputLen
=
data
.
length
;
ByteArrayOutputStream
out
=
new
ByteArrayOutputStream();
int
offSet
= 0;
byte
[]
cache
;
int
i
= 0;
// 對數據分段加密
while
(
inputLen
-
offSet
> 0)
{
if
(
inputLen
-
offSet
>
MAX_ENCRYPT_BLOCK
)
{
cache
=
cipher
.doFinal(
data
,
offSet
,
MAX_ENCRYPT_BLOCK
);
}
else
{
cache
=
cipher
.doFinal(
data
,
offSet
,
inputLen
-
offSet
);
}
out
.write(
cache
, 0,
cache
.
length
);
i
++;
offSet
=
i
*
MAX_ENCRYPT_BLOCK
;
}
byte
[]
encryptedData
=
out
.toByteArray();
out
.close();
return
encryptedData
;
}
即把超過117(加密)和128(解密)長度的原文內容分割成多個部分,依次加解密,再合並.
參考下面文件
