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
  98 - (void)encodeWithCoder:(NSCoder *)aCoder {
  99     [aCoder encodeBool: self.asSender forKey:KCDSSender];
 100     [aCoder encodeObject: self.secret forKey:KCDSSecret];
 101     [aCoder encodeInt64: self.context forKey:KCDSContext];
 102 }
 103
 104 - (nullable instancetype)initWithCoder:(NSCoder *)aDecoder {
 105
 106     bool asSender = [aDecoder decodeBoolForKey:KCDSSender];
 107     NSData* secret = [aDecoder decodeObjectOfClass:[NSData class] forKey:KCDSSecret];
 108     uint64_t context = [aDecoder decodeInt64ForKey:KCDSContext];
 109
 110     return [self initWithSecret:secret context:context as:asSender];
 111 }
 112
 113 + (BOOL)supportsSecureCoding {
 114     return true;
 115 }
 116
 117
 118
 119 - (nullable instancetype) initAsSender: (NSData*) sharedSecret context: (uint64_t) context {
 120     return [self initWithSecret:sharedSecret context:context as:true];
 121 }
 122
 123 - (nullable instancetype) initAsReceiver: (NSData*) sharedSecret context: (uint64_t) context {
 124     return [self initWithSecret:sharedSecret context:context as:false];
 125 }
 126
 127 - (nullable instancetype) initWithSecret: (NSData*) sharedSecret
 128                                  context: (uint64_t) context
 129                                       as: (bool) sender {
 130     static dispatch_once_t onceToken;
 131     dispatch_once(&onceToken, ^{
 132         kdfInfoSendToReceive = [NSData dataWithBytesNoCopy: kdfInfoForwardString
 133                                                     length: strlen(kdfInfoForwardString)
 134                                               freeWhenDone: false];
 135
 136         kdfInfoReceiveToSend = [NSData dataWithBytesNoCopy: kdfInfoBackwardString
 137                                                     length: strlen(kdfInfoBackwardString)
 138                                               freeWhenDone: false];
 139     });
 140
 141     self = [super init];
 142
 143     self.asSender = sender;
 144     self.secret = sharedSecret;
 145     self.send = malloc(ccgcm_context_size(ccaes_gcm_encrypt_mode()));
 146     self.receive = malloc(ccgcm_context_size(ccaes_gcm_decrypt_mode()));
 147     self.context = context;
 148
 149     if (self.send == nil || self.receive == nil) {
 150         return nil;
 151     }
 152
 153     derive_and_init(ccaes_gcm_encrypt_mode(),
 154                     self.send, self.secret,
 155                     sender ? kdfInfoSendToReceive : kdfInfoReceiveToSend);
 156     derive_and_init(ccaes_gcm_decrypt_mode(),
 157                     self.receive, self.secret,
 158                     !sender ? kdfInfoSendToReceive : kdfInfoReceiveToSend);
 159
 160     return self;
 161 }
 162
 163 - (size_t) encryptCapsuleSize: (NSData*) plaintext IV: (NSData*) iv {
 164     size_t iv_size = kcder_sizeof_data(iv, nil);
 165     if (iv_size == 0) {
 166         return 0;
 167     }
 168     size_t text_size = kcder_sizeof_data(plaintext, nil);
 169     if (text_size == 0) {
 170         return 0;
 171     }
 172     size_t tag_size = kcder_sizeof_data([NSMutableData dataWithLength: kKCAESGCMTagSize], nil);
 173     if (tag_size == 0) {
 174         return 0;
 175     }
 176     return ccder_sizeof(CCDER_CONSTRUCTED_SEQUENCE, iv_size + text_size + tag_size);
 177 }
 178
 179 - (bool) GCM:(const struct ccmode_gcm*) mode
 180      context:(ccgcm_ctx*) ctx
 181           iv:(NSData*) iv
 182         size:(size_t) data_size
 183         data:(const uint8_t*) data
 184    processed:(uint8_t*) result
 185          tag:(uint8_t*) tagBuffer
 186        error:(NSError**) error {
 187     int cc_status;
 188
 189     cc_status = ccgcm_reset(mode, ctx);
 190     if (!CoreCryptoError(cc_status, error, @"ccgcm_reset failed: %d", cc_status))
 191       return NO;
 192
 193     cc_status = ccgcm_set_iv(mode, ctx, iv.length, iv.bytes);
 194     if (!CoreCryptoError(cc_status, error, @"ccgcm_set_iv failed: %d", cc_status))
 195       return NO;
 196
 197     cc_status = ccgcm_update(mode, ctx, data_size, data, result);
 198     if (!CoreCryptoError(cc_status, error, @"ccgcm_update failed: %d", cc_status))
 199       return NO;
 200
 201     cc_status = ccgcm_finalize(mode, ctx, kKCAESGCMTagSize, tagBuffer);
 202     return CoreCryptoError(cc_status, error, @"ccgcm_finalize failed: %d", cc_status);
 203 }
 204
 205
 206 - (nullable NSData*) encrypt: (NSData*) data error: (NSError**) error {
 207     static const int kIVSizeInBytes = 16;
 208
 209     NSMutableData* iv = [NSMutableData dataWithRandomBytes: kIVSizeInBytes];
 210
 211     NSMutableData* result = [NSMutableData dataWithLength: [self encryptCapsuleSize: data IV: iv]];
 212
 213     // Encode with all the space set up for the result:
 214
 215     uint8_t* der_end = result.mutableBytes + result.length;
 216     const uint8_t* der = result.bytes;
 217
 218     uint8_t* tag = NULL;
 219     uint8_t* encrypted = NULL;
 220
 221     der_end = ccder_encode_constructed_tl(CCDER_CONSTRUCTED_SEQUENCE, der_end, der,
 222               kcder_encode_data(iv, error, der,
 223               kcder_encode_raw_octet_space(data.length, &encrypted, der,
 224               kcder_encode_raw_octet_space(kKCAESGCMTagSize, &tag, der, der_end))));
 225
 226     if (der_end != der) {
 227         KCJoiningErrorCreate(kAllocationFailure, error, @"Failed to allocate space for der");
 228         return nil;
 229     }
 230
 231     const struct ccmode_gcm * mode = ccaes_gcm_encrypt_mode();
 232
 233     return [self GCM:mode
 234              context:self.send
 235                   iv:iv
 236                 size:data.length
 237                 data:data.bytes
 238            processed:encrypted
 239                  tag:tag
 240                error:error] ? result : nil;
 241 }
 242
 243 - (nullable NSData*) decryptAndVerify: (NSData*) data error: (NSError**) error {
 244
 245     const uint8_t *der = data.bytes;
 246     const uint8_t *der_end = der + data.length;
 247
 248     const uint8_t *sequence_end = 0;
 249     der = ccder_decode_constructed_tl(CCDER_CONSTRUCTED_SEQUENCE, &sequence_end, der, der_end);
 250
 251     if (der == NULL || sequence_end != der_end) {
 252         KCJoiningErrorCreate(kDERUnknownEncoding, error, @"decode failed");
 253         return nil;
 254     }
 255
 256     const uint8_t *encrypted = 0;
 257     size_t encrypted_len = 0;
 258     const uint8_t *received_tag = 0;
 259
 260     NSData* iv;
 261
 262     der = kcder_decode_data(&iv, error, der, der_end);
 263     if (der == NULL) return nil;
 264
 265     encrypted = ccder_decode_constructed_tl(CCDER_OCTET_STRING, &der, der, der_end);
 266     encrypted_len = der - encrypted;
 267
 268     received_tag = ccder_decode_constructed_tl(CCDER_OCTET_STRING, &der, der, der_end);
 269
 270     if (der == NULL) {
 271         KCJoiningErrorCreate(kDERUnknownEncoding, error, @"Decode failure");
 272         return nil;
 273     }
 274
 275     if (der != der_end) {
 276         KCJoiningErrorCreate(kDERUnknownEncoding, error, @"Extra space");
 277         return nil;
 278     }
 279
 280     if (der - received_tag != kKCAESGCMTagSize) {
 281         KCJoiningErrorCreate(kDERUnknownEncoding, error, @"Unexpected tag size: %ld", (long)(der - received_tag));
 282         return nil;
 283     }
 284
 285     NSMutableData* decrypted = [NSMutableData dataWithLength: encrypted_len];
 286
 287     uint8_t tag[kKCAESGCMTagSize];
 288     memcpy(tag, received_tag, sizeof(tag));
 289
 290     const struct ccmode_gcm * mode = ccaes_gcm_decrypt_mode();
 291
 292     return [self GCM:mode
 293              context:self.receive
 294                   iv:iv
 295                 size:encrypted_len
 296                 data:encrypted
 297            processed:decrypted.mutableBytes
 298                  tag:tag
 299                error:error] ? decrypted : nil;
 300 }
 301
 302 - (void) finalize {
 303     if (self.send) {
 304         ccgcm_ctx_clear(sizeof(*self.send), self.send);
 305         free(self.send);
 306     }
 307     if (self.receive) {
 308         ccgcm_ctx_clear(sizeof(*self.receive), self.receive);
 309         free(self.receive);
 310     }
 311     [super finalize];
 312 }
 313
 314 @end