KeychainCircle/KCAESGCMDuplexSession.m

   1 //
   2 //  KCAESGCMDuplexSession.m
   3 //  Security
   4 //
   5 //
   6
   7 #import <KeychainCircle/KCAESGCMDuplexSession.h>
   8 #import <KeychainCircle/KCDer.h>
   9 #import <KeychainCircle/KCError.h>
  10 #import <NSError+KCCreationHelpers.h>
  11 #import <NSData+SecRandom.h>
  12
  13 #include <corecrypto/ccaes.h>
  14 #include <corecrypto/ccmode.h>
  15 #include <corecrypto/cchkdf.h>
  16 #include <corecrypto/ccsha2.h>
  17
  18 #include <corecrypto/ccder.h>
  19
  20 #include <libkern/OSByteOrder.h>
  21
  22
  23 #define kdfInfoForwardString "send->recv"
  24 #define kdfInfoBackwardString "recv->send"
  25 static NSData* kdfInfoSendToReceive = nil;
  26 static NSData* kdfInfoReceiveToSend = nil;
  27
  28 static const int kKCAESGCMTagSize = CCAES_KEY_SIZE_128;
  29 static const int kKCAESGCMKeySize = CCAES_KEY_SIZE_128;
  30
  31 static bool derive_and_init(const struct ccmode_gcm *mode, ccgcm_ctx* ctx, NSData* sharedSecret, NSData* info) {
  32     const struct ccdigest_info *di = ccsha256_di();
  33
  34     NSMutableData* space = [NSMutableData dataWithLength:di->output_size];
  35
  36     int cc_status = 0;
  37
  38     cc_status = cchkdf(di,
  39                        sharedSecret.length, sharedSecret.bytes,
  40                        0, NULL,
  41                        info.length, info.bytes,
  42                        space.length, space.mutableBytes);
  43
  44     if (cc_status != 0) {
  45         return false;
  46     }
  47     // We only use the first 16 bytes (128 bits) for the key.
  48     cc_status = ccgcm_init(mode, ctx, kKCAESGCMKeySize, space.bytes);
  49     cc_clear(space.length, space.mutableBytes);
  50
  51     return cc_status == 0;
  52 }
  53
  54 @interface NSMutableData(KAESGCM)
  55 - (void) replaceTrailingWith7LSB: (uint64_t) value;
  56 @end
  57
  58 @implementation NSMutableData(KAESGCM)
  59 - (void) replaceTrailingWith7LSB: (uint64_t) value {
  60     uint8_t bytes[sizeof(value)];
  61     OSWriteBigInt64(bytes, 0, value);
  62
  63     [self replaceBytesInRange: NSMakeRange(self.length - 7, 7) withBytes: (bytes + 1)];
  64 }
  65 @end
  66
  67
  68
  69 @interface KCAESGCMDuplexSession ()
  70 @property (readwrite) bool asSender;
  71 @property (readwrite) uint64_t context;
  72 @property (readwrite) NSData* secret;
  73
  74 @property (readwrite) ccgcm_ctx * send;
  75 @property (readwrite) ccgcm_ctx * receive;
  76
  77 @end
  78
  79 @implementation KCAESGCMDuplexSession
  80
  81 + (nullable instancetype) sessionAsSender: (NSData*) sharedSecret
  82                                   context: (uint64_t) context {
  83     return [[KCAESGCMDuplexSession alloc] initAsSender:sharedSecret
  84                                                context:context];
  85 }
  86
  87 + (nullable instancetype) sessionAsReceiver: (NSData*) sharedSecret
  88                                     context: (uint64_t) context {
  89     return [[KCAESGCMDuplexSession alloc] initAsReceiver:sharedSecret
  90                                                  context:context];
  91
  92 }
  93
  94 static NSString* KCDSSender = @"asSender";
  95 static NSString* KCDSSecret = @"secret";
  96 static NSString* KCDSContext = @"context";
  97 static NSString* KCDSPairingUUID = @"uuid";
  98 static NSString* KCDSPiggybackingVersion = @"piggy";
  99 static NSString* KCDSEpoch= @"epoch";
 100
 101 - (void)encodeWithCoder:(NSCoder *)aCoder {
 102     [aCoder encodeBool: self.asSender forKey:KCDSSender];
 103     [aCoder encodeObject: self.secret forKey:KCDSSecret];
 104     [aCoder encodeInt64: self.context forKey:KCDSContext];
 105     [aCoder encodeObject: self.pairingUUID forKey:KCDSPairingUUID];
 106     [aCoder encodeInt64: self.piggybackingVersion forKey:KCDSPiggybackingVersion];
 107     [aCoder encodeInt64:self.epoch forKey:KCDSEpoch];
 108 }
 109
 110 - (nullable instancetype)initWithCoder:(NSCoder *)aDecoder {
 111     bool asSender = [aDecoder decodeBoolForKey:KCDSSender];
 112     NSData* secret = [aDecoder decodeObjectOfClass:[NSData class] forKey:KCDSSecret];
 113     uint64_t context = [aDecoder decodeInt64ForKey:KCDSContext];
 114
 115     NSString* pairingUUID = [aDecoder decodeObjectOfClass:[NSString class] forKey:KCDSPairingUUID];
 116     uint64_t piggybackingVersion = [aDecoder decodeInt64ForKey:KCDSPiggybackingVersion];
 117     uint64_t epoch = [aDecoder decodeInt64ForKey:KCDSEpoch];
 118
 119     return [self initWithSecret:secret context:context as:asSender pairingUUID:pairingUUID piggybackingVersion:piggybackingVersion epoch:epoch];
 120 }
 121
 122 + (BOOL)supportsSecureCoding {
 123     return true;
 124 }
 125
 126
 127
 128 - (nullable instancetype) initAsSender: (NSData*) sharedSecret context: (uint64_t) context {
 129     return [self initWithSecret:sharedSecret context:context as:true];
 130 }
 131
 132 - (nullable instancetype) initAsReceiver: (NSData*) sharedSecret context: (uint64_t) context {
 133     return [self initWithSecret:sharedSecret context:context as:false];
 134 }
 135
 136 - (nullable instancetype) initWithSecret: (NSData*) sharedSecret
 137                                  context: (uint64_t) context
 138                                       as: (bool) sender {
 139     return [self initWithSecret:sharedSecret
 140                         context:context
 141                              as:sender
 142                     pairingUUID:nil
 143             piggybackingVersion:0
 144                           epoch:1];
 145 }
 146
 147 - (nullable instancetype)initWithSecret:(NSData*)sharedSecret
 148                                 context:(uint64_t)context
 149                                      as:(bool) sender
 150                             pairingUUID:(NSString* _Nullable)pairingUUID
 151                     piggybackingVersion:(uint64_t)piggybackingVersion
 152                                   epoch:(uint64_t)epoch
 153 {
 154     static dispatch_once_t onceToken;
 155     dispatch_once(&onceToken, ^{
 156         kdfInfoSendToReceive = [NSData dataWithBytesNoCopy: kdfInfoForwardString
 157                                                     length: strlen(kdfInfoForwardString)
 158                                               freeWhenDone: false];
 159
 160         kdfInfoReceiveToSend = [NSData dataWithBytesNoCopy: kdfInfoBackwardString
 161                                                     length: strlen(kdfInfoBackwardString)
 162                                               freeWhenDone: false];
 163     });
 164
 165     self = [super init];
 166
 167     self.asSender = sender;
 168     self.secret = sharedSecret;
 169     self.send = malloc(ccgcm_context_size(ccaes_gcm_encrypt_mode()));
 170     self.receive = malloc(ccgcm_context_size(ccaes_gcm_decrypt_mode()));
 171     self.context = context;
 172
 173     _pairingUUID = pairingUUID;
 174     _piggybackingVersion = piggybackingVersion;
 175     _epoch = epoch;
 176
 177     if (self.send == nil || self.receive == nil) {
 178         return nil;
 179     }
 180
 181     derive_and_init(ccaes_gcm_encrypt_mode(),
 182                     self.send, self.secret,
 183                     sender ? kdfInfoSendToReceive : kdfInfoReceiveToSend);
 184     derive_and_init(ccaes_gcm_decrypt_mode(),
 185                     self.receive, self.secret,
 186                     !sender ? kdfInfoSendToReceive : kdfInfoReceiveToSend);
 187
 188     return self;
 189 }
 190
 191 - (size_t) encryptCapsuleSize: (NSData*) plaintext IV: (NSData*) iv {
 192     size_t iv_size = kcder_sizeof_data(iv, nil);
 193     if (iv_size == 0) {
 194         return 0;
 195     }
 196     size_t text_size = kcder_sizeof_data(plaintext, nil);
 197     if (text_size == 0) {
 198         return 0;
 199     }
 200     size_t tag_size = kcder_sizeof_data([NSMutableData dataWithLength: kKCAESGCMTagSize], nil);
 201     if (tag_size == 0) {
 202         return 0;
 203     }
 204     return ccder_sizeof(CCDER_CONSTRUCTED_SEQUENCE, iv_size + text_size + tag_size);
 205 }
 206
 207 - (bool) GCM:(const struct ccmode_gcm*) mode
 208      context:(ccgcm_ctx*) ctx
 209           iv:(NSData*) iv
 210         size:(size_t) data_size
 211         data:(const uint8_t*) data
 212    processed:(uint8_t*) result
 213          tag:(uint8_t*) tagBuffer
 214        error:(NSError**) error {
 215     int cc_status;
 216
 217     cc_status = ccgcm_reset(mode, ctx);
 218     if (!CoreCryptoError(cc_status, error, @"ccgcm_reset failed: %d", cc_status))
 219       return NO;
 220
 221     cc_status = ccgcm_set_iv(mode, ctx, iv.length, iv.bytes);
 222     if (!CoreCryptoError(cc_status, error, @"ccgcm_set_iv failed: %d", cc_status))
 223       return NO;
 224
 225     cc_status = ccgcm_update(mode, ctx, data_size, data, result);
 226     if (!CoreCryptoError(cc_status, error, @"ccgcm_update failed: %d", cc_status))
 227       return NO;
 228
 229     cc_status = ccgcm_finalize(mode, ctx, kKCAESGCMTagSize, tagBuffer);
 230     return CoreCryptoError(cc_status, error, @"ccgcm_finalize failed: %d", cc_status);
 231 }
 232
 233
 234 - (nullable NSData*) encrypt: (NSData*) data error: (NSError**) error {
 235     static const int kIVSizeInBytes = 16;
 236
 237     NSMutableData* iv = [NSMutableData dataWithRandomBytes: kIVSizeInBytes];
 238
 239     NSMutableData* result = [NSMutableData dataWithLength: [self encryptCapsuleSize: data IV: iv]];
 240
 241     // Encode with all the space set up for the result:
 242
 243     uint8_t* der_end = result.mutableBytes + result.length;
 244     const uint8_t* der = result.bytes;
 245
 246     uint8_t* tag = NULL;
 247     uint8_t* encrypted = NULL;
 248
 249     der_end = ccder_encode_constructed_tl(CCDER_CONSTRUCTED_SEQUENCE, der_end, der,
 250               kcder_encode_data(iv, error, der,
 251               kcder_encode_raw_octet_space(data.length, &encrypted, der,
 252               kcder_encode_raw_octet_space(kKCAESGCMTagSize, &tag, der, der_end))));
 253
 254     if (der_end != der) {
 255         KCJoiningErrorCreate(kAllocationFailure, error, @"Failed to allocate space for der");
 256         return nil;
 257     }
 258
 259     const struct ccmode_gcm * mode = ccaes_gcm_encrypt_mode();
 260
 261     return [self GCM:mode
 262              context:self.send
 263                   iv:iv
 264                 size:data.length
 265                 data:data.bytes
 266            processed:encrypted
 267                  tag:tag
 268                error:error] ? result : nil;
 269 }
 270
 271 - (nullable NSData*) decryptAndVerify: (NSData*) data error: (NSError**) error {
 272
 273     const uint8_t *der = data.bytes;
 274     const uint8_t *der_end = der + data.length;
 275
 276     const uint8_t *sequence_end = 0;
 277     der = ccder_decode_constructed_tl(CCDER_CONSTRUCTED_SEQUENCE, &sequence_end, der, der_end);
 278
 279     if (der == NULL || sequence_end != der_end) {
 280         KCJoiningErrorCreate(kDERUnknownEncoding, error, @"decode failed");
 281         return nil;
 282     }
 283
 284     const uint8_t *encrypted = 0;
 285     size_t encrypted_len = 0;
 286     const uint8_t *received_tag = 0;
 287
 288     NSData* iv;
 289
 290     der = kcder_decode_data(&iv, error, der, der_end);
 291     if (der == NULL) return nil;
 292
 293     encrypted = ccder_decode_constructed_tl(CCDER_OCTET_STRING, &der, der, der_end);
 294     encrypted_len = der - encrypted;
 295
 296     received_tag = ccder_decode_constructed_tl(CCDER_OCTET_STRING, &der, der, der_end);
 297
 298     if (der == NULL) {
 299         KCJoiningErrorCreate(kDERUnknownEncoding, error, @"Decode failure");
 300         return nil;
 301     }
 302
 303     if (der != der_end) {
 304         KCJoiningErrorCreate(kDERUnknownEncoding, error, @"Extra space");
 305         return nil;
 306     }
 307
 308     if (der - received_tag != kKCAESGCMTagSize) {
 309         KCJoiningErrorCreate(kDERUnknownEncoding, error, @"Unexpected tag size: %ld", (long)(der - received_tag));
 310         return nil;
 311     }
 312
 313     NSMutableData* decrypted = [NSMutableData dataWithLength: encrypted_len];
 314
 315     uint8_t tag[kKCAESGCMTagSize];
 316     memcpy(tag, received_tag, sizeof(tag));
 317
 318     const struct ccmode_gcm * mode = ccaes_gcm_decrypt_mode();
 319
 320     return [self GCM:mode
 321              context:self.receive
 322                   iv:iv
 323                 size:encrypted_len
 324                 data:encrypted
 325            processed:decrypted.mutableBytes
 326                  tag:tag
 327                error:error] ? decrypted : nil;
 328 }
 329
 330 #pragma clang diagnostic push
 331 #pragma clang diagnostic ignored "-Wdeprecated-implementations"
 332 - (void) finalize {
 333     if (self.send) {
 334         ccgcm_ctx_clear(sizeof(*self.send), self.send);
 335         free(self.send);
 336     }
 337     if (self.receive) {
 338         ccgcm_ctx_clear(sizeof(*self.receive), self.receive);
 339         free(self.receive);
 340     }
 341     [super finalize];
 342 }
 343 #pragma clang diagnostic pop
 344
 345 @end