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MYCrypto / MYPublicKey.h

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//
//  MYPublicKey.h
//  MYCrypto
//
//  Created by Jens Alfke on 3/25/09.
//  Copyright 2009 Jens Alfke. All rights reserved.
//

#import "MYKey.h"
@class MYSHA1Digest, MYSymmetricKey, MYCertificate;

#if !TARGET_OS_IPHONE
#import <Security/SecKey.h>
#endif


/** A public key, which can be used for encrypting data and verifying signatures.
    MYPublicKeys are created as part of generating a key-pair, 
    or by being imported from data into a MYKeychain. */
@interface MYPublicKey : MYKey
{
    @private
    MYSHA1Digest *_digest;              // The key's SHA-1 digest (null if not determined yet)
    MYCertificate *_certificate;        // The cert this key came from (if any)
}

/** The public key's SHA-1 digest. This is a convenient short (20-byte) identifier for the key. */
@property (readonly) MYSHA1Digest *publicKeyDigest;

/** Encrypts a short piece of data using this key, returning the raw encrypted result.
    An RSA key can encrypt only blocks smaller than its own key size; this
    method will fail and return nil if the data is too long.
    RSA encryption is also much slower than regular symmetric-key encryption, so the correct
    way to encrypt a large block of data using a public key is to first generate a random
    symmetric key, called the "session key" (using a Cryptor), encrypt that session key with the 
    public key, and then encrypt your data with the session key. Send the encrypted session key
    and the encrypted data. */
- (NSData*) rawEncryptData: (NSData*)data;

/** Verifies the signature of a block of data. If the result is YES, you can be assured that
    the signature was generated from the data by using this key's matching private key.
    If the result is NO, something is wrong: either the data or the signature was modified,
    or the signature was generated by a different private key.
    (What's actually verified using RSA is the SHA-1 digest of the data.) */
- (BOOL) verifySignature: (NSData*)signature ofData: (NSData*)data;


/** @name Expert
 *  Advanced methods. 
 */
//@{

/** Initializes a public key directly from its raw RSA modulus and exponent.
    These numbers must come from an existing key-pair generated by the RSA algorithm; 
    you CANNOT just pass in random data and create a working key! (To create a new key pair,
    call -[MYKeychain generateRSAKeyPairOfSize:].)
    @param modulus  RSA modulus, a very large integer represented as a blob of big-endian data.
    @param exponent  RSA exponent, a prime number, commonly 17 or 65537.
*/
- (id) initWithModulus: (NSData*)modulus exponent: (unsigned)exponent;

/** Retrieves the raw RSA modulus and exponent, which together uniquely specify the key.
    The length of the modulus is the size, in bits, of the key: for example, a 2048-bit key
    has 256 bytes of modulus data.
    @param outModulus  On return, will contain the modulus: a very large positive integer represented
                       as a blob of unsigned big-endian data.
    @param outExponent  On return, will contain the exponent: a prime number, often 17 or 65537. */
- (BOOL) getModulus: (NSData**)outModulus exponent: (unsigned*)outExponent;

#if !TARGET_OS_IPHONE

/** Verifies a signature, using the specified signature algorithm, for example
    CSSM_ALGID_SHA1WithRSA, CSSM_ALGID_SHA256WithRSA or CSSM_ALGID_MD5WithRSA. */
- (BOOL) verifySignature: (NSData*)signature 
                  ofData: (NSData*)data
           withAlgorithm: (CSSM_ALGORITHMS)algorithm;

/** Encrypts a session key using this public key. 
    The holder of the private key can then unwrap the session key from this data.
    @param sessionKey  The symmetric session key to wrap/encrypt
    @return  The encrypted data representing the session key */
- (NSData*) wrapSessionKey: (MYSymmetricKey*)sessionKey;

#endif
//@}

@end