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    openssl_public_decrypt

    (PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)

    openssl_public_decrypt — Desencripta información con la clave pública

    Descripción

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

    openssl_public_decrypt() desencripta la información data que fue previamente encriptada mediante openssl_private_encrypt() y almacena el resultado en decrypted.

    Se puede usar esta función para, p.ej., verificar si el mensaje fué escrito por el propietario de la clave privada.

    Parámetros

    data

    decrypted

    key

    key debe ser la clave pública que se corresponde con la usada para encriptar la información.

    padding

    padding puede ser OPENSSL_PKCS1_PADDING, OPENSSL_NO_PADDING.

    Valores devueltos

    Devuelve true en caso de éxito o false en caso de error.

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    User Contributed Notes 1 note

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    5
    Hernanibus
    8 years ago
    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;
    }
    ?>
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