note 119811 added to function.openssl-public-decrypt

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; } ?> ---- Server IP: 49.212.134.217 Probable Submitter: 157.65.39.189 ---- Manual Page -- http://php.net/manual/en/function.openssl-public-decrypt.php Edit -- https://master.php.net/note/edit/119811 Del: integrated -- https://master.php.net/note/delete/119811/integrated Del: useless -- https://master.php.net/note/delete/119811/useless Del: bad code -- https://master.php.net/note/delete/119811/bad+code Del: spam -- https://master.php.net/note/delete/119811/spam Del: non-english -- https://master.php.net/note/delete/119811/non-english Del: in docs -- https://master.php.net/note/delete/119811/in+docs Del: other reasons-- https://master.php.net/note/delete/119811 Reject -- https://master.php.net/note/reject/119811 Search -- https://master.php.net/manage/user-notes.php