Why delete publicExponent from PUBLIC_RAW key?

[spacewrench]

I have an RSA modulus and public-key exponent stored in a database as hex strings. I've managed to get them into a phpseclib RSA key:

Code: Select all

$rsa = new Crypt_RSA( );
$rsa->loadKey( array( 'n' => new Math_BigInteger( 'modulus hex string', 16 ),
                                'e' => new Math_BigInteger( 'pub exponent', 16 ) ),
                       CRYPT_RSA_PUBLIC_FORMAT_RAW );

and I can encrypt using the key. However, I'd also like to be able to print out the public key in PKCS1 format, but when I try, getPublicKey() returns false. After investigating, it appears that loadKey moves ['publicExponent'] to ['exponent'] and sets ['publicExponent'] to false (RSA.php:1193).

Why is that?

[TerraFrost]

Some private keys can be indistinguishable from public keys. In those cases calling getPublicKey() doesn't make a lot of sense.

As of the 0.2.2 release getPublicKey() can only be called when the key is clearly a private key and has a corresponding public key.

As of the latest github.com version even regular public keys can be treated as public keys if you do $rsa->setPublicKey() first.

As for why publicExponent is unset... the above is why. Because some private keys can be indistinguishable for regular keys.