openssl_public_decrypt()

(PHP 4 >= 4.0.6, PHP 5, PHP 7)

使用公钥解密数据

说明

openssl_public_decrypt(string $data,string &$decrypted, mixed $key[,int $padding= OPENSSL_PKCS1_PADDING]): bool

openssl_public_decrypt()解密先前由openssl_private_encrypt()加密的数据$data并且将结果保存至变量$decrypted中。

你可以用该函数来校验消息是否是私钥拥有者写的。

参数

$data
$decrypted
$key: $key必须是和用来加密数据的私钥配对的公钥。
$padding: $padding可以是如下至OPENSSL_PKCS1_PADDING,OPENSSL_NO_PADDING.

返回值

成功时返回TRUE，或者在失败时返回FALSE。

参见

openssl_private_encrypt()使用私钥加密数据
openssl_private_decrypt()使用私钥解密数据

Just a little note on [P.Peyremorte]'s note in manual's openssl_private_encrypt.
"- openssl_private_encrypt can encrypt a maximum of 117 chars at one time."
This depends on the length of $key:
- For a 1024 bit key length => max number of chars (bytes) to encrypt = 1024/8 - 11(when padding used) = 117 chars (bytes).
- For a 2048 bit key length => max number of chars (bytes) to encrypt = 2048/8 - 11(when padding used) = 245 chars (bytes).
... and so on
By the way, if openssl_private_encrypt fails because of data size you won't get anything but just false as returned value, the same for openssl_public_decrypt() on decryption.
"- the encrypted output string is always 129 char length. If you use base64_encode on the encrypted output, it will give always 172 chars, with the last always "=" (filler)"
This again depends on the length of $key:
- For a 1024 bit key length => encrypted number of raw bytes is always a block of 128 bytes (1024 bits) by RSA design.
- For a 2048 bit key length => encrypted number of raw bytes is always a block of 256 bytes (2048 bits) by RSA design.
... and so on
About base64_encode output length, it depends on what you encode (meaning it depends on the bytes resulting after encryption), but in general the resulting encoded string will be about a 33% bigger (for 128 bytes bout 170 bytes and for 256 bytes about 340 bytes).
I would then generalize a little [P.Peyremorte]'s note by:
<?php
// given the variables as constants:
 //Block size for encryption block cipher
 private $ENCRYPT_BLOCK_SIZE = 200;// this for 2048 bit key for example, leaving some room
 //Block size for decryption block cipher
 private $DECRYPT_BLOCK_SIZE = 256;// this again for 2048 bit key
     //For encryption we would use:
 function encrypt_RSA($plainData, $privatePEMKey)
 {
  $encrypted = '';
  $plainData = str_split($plainData, $this->ENCRYPT_BLOCK_SIZE);
  foreach($plainData as $chunk)
  {
   $partialEncrypted = '';
   //using for example OPENSSL_PKCS1_PADDING as padding
   $encryptionOk = openssl_private_encrypt($chunk, $partialEncrypted, $privatePEMKey, OPENSSL_PKCS1_PADDING);
   if($encryptionOk === false){return false;}//also you can return and error. If too big this will be false
   $encrypted .= $partialEncrypted;
  }
  return base64_encode($encrypted);//encoding the whole binary String as MIME base 64
 }
     //For decryption we would use:
 protected function decrypt_RSA($publicPEMKey, $data)
 {
  $decrypted = '';
  //decode must be done before spliting for getting the binary String
  $data = str_split(base64_decode($data), $this->DECRYPT_BLOCK_SIZE);
  foreach($data as $chunk)
  {
   $partial = '';
   //be sure to match padding
   $decryptionOK = openssl_public_decrypt($chunk, $partial, $publicPEMKey, OPENSSL_PKCS1_PADDING);
   if($decryptionOK === false){return false;}//here also processed errors in decryption. If too big this will be false
   $decrypted .= $partial;
  }
  return $decrypted;
 }
?>

Encrypt using private key, decrypt using public key.
Use this for posting signed messages: Anyone with access to
your public key can read it, but they can't create one with
your signature.
<?php
echo "Source: $source";
$fp=fopen("/path/to/private.key","r");
$priv_key=fread($fp,8192);
fclose($fp);
// $passphrase is required if your key is encoded (suggested)
$res = openssl_get_privatekey($priv_key,$passphrase);
/*
 * NOTE: Here you use the returned resource value
 */
openssl_private_encrypt($source,$crypttext,$res);
echo "String crypted: $crypttext";
$fp=fopen ("/path/to/certificate.crt","r");
$pub_key=fread($fp,8192);
fclose($fp);
openssl_get_publickey($pub_key);
/*
 * NOTE: Here you use the $pub_key value (converted, I guess)
 */
openssl_public_decrypt($crypttext,$newsource,$pub_key);
echo "String decrypt : $newsource";
?>

<?php
$fp=fopen ("/path/to/certificato.pem");
$pub_key=fread ($fp,8192);
openssl_get_publickey ($pub_key);
openssl_public_decrypt ($source,$finaltext,$pub_key);
echo "String decrypt : $finaltext";
?>