implementation of PRAGMA cipher_integrity_check and associated tests

sjlombardo · sjlombardo · commit 488d81e8da2d · 2019-05-15T10:24:27.000-04:00
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,6 +1,9 @@
 # SQLCipher Change Log
 All notable changes to this project will be documented in this file.
 
+## [unreleased] - (TBD - [unreleased])
+-  Adds PRAGMA cipher_integrity_check to perform external verification of page HMACs
+
 ## [4.1.0] - (March 2019 - [4.1.0 changes])
 - Defer reading salt from header until key derivation is triggered
 - Clarify usage of sqlite3_rekey for plaintext databases in header
diff --git a/src/crypto.c b/src/crypto.c
@@ -629,6 +629,11 @@ int sqlcipher_codec_pragma(sqlite3* db, int iDb, Parse *pParse, const char *zLef
       pragma = sqlite3_mprintf("PRAGMA cipher_default_kdf_algorithm = %s;", SQLCIPHER_PBKDF2_HMAC_SHA512_LABEL);
     }
     codec_vdbe_return_string(pParse, "pragma", pragma, P4_DYNAMIC);
+  }else
+  if( sqlite3StrICmp(zLeft,"cipher_integrity_check")==0 ){
+    if(ctx) {
+      sqlcipher_codec_ctx_integrity_check(ctx, pParse, "cipher_integrity_check");
+    }
   }else {
     return 0;
   }
diff --git a/src/crypto.h b/src/crypto.h
@@ -289,6 +289,8 @@ int sqlcipher_get_mem_security(void);
 
 int sqlcipher_find_db_index(sqlite3 *db, const char *zDb);
 
+int sqlcipher_codec_ctx_integrity_check(codec_ctx *, Parse *, char *);
+
 #endif
 #endif
 /* END SQLCIPHER */
diff --git a/src/crypto_impl.c b/src/crypto_impl.c
@@ -1254,6 +1254,87 @@ static int sqlcipher_check_connection(const char *filename, char *key, int key_s
   return rc;
 }
 
+int sqlcipher_codec_ctx_integrity_check(codec_ctx *ctx, Parse *pParse, char *column) {
+  Pgno page = 1;
+  int i, trans_rc, rc = 0;
+  char *result;
+  unsigned char *hmac_out = NULL;
+  sqlite3_file *fd = sqlite3PagerFile(ctx->pBt->pBt->pPager);
+  i64 file_sz;
+
+  Vdbe *v = sqlite3GetVdbe(pParse);
+  sqlite3VdbeSetNumCols(v, 1);
+  sqlite3VdbeSetColName(v, 0, COLNAME_NAME, column, SQLITE_STATIC);
+
+  if(fd == NULL || fd->pMethods == 0) {
+    sqlite3VdbeAddOp4(v, OP_String8, 0, 1, 0, "database file is undefined", P4_TRANSIENT);
+    sqlite3VdbeAddOp2(v, OP_ResultRow, 1, 1);
+    goto cleanup;
+  }
+
+  if(!(ctx->flags & CIPHER_FLAG_HMAC)) {
+    sqlite3VdbeAddOp4(v, OP_String8, 0, 1, 0, "HMAC is not enabled, unable to integrity check", P4_TRANSIENT);
+    sqlite3VdbeAddOp2(v, OP_ResultRow, 1, 1);
+    goto cleanup;
+  }
+
+  if((rc = sqlcipher_codec_key_derive(ctx)) != SQLITE_OK) {
+    sqlite3VdbeAddOp4(v, OP_String8, 0, 1, 0, "unable to derive keys", P4_TRANSIENT);
+    sqlite3VdbeAddOp2(v, OP_ResultRow, 1, 1);
+    goto cleanup;
+  }
+
+  /* establish an exclusive lock on the database */
+  if((trans_rc = sqlite3BtreeBeginTrans(ctx->pBt, 2, 0)) != SQLITE_OK) {
+    sqlite3VdbeAddOp4(v, OP_String8, 0, 1, 0, "unable to lock database", P4_TRANSIENT);
+    sqlite3VdbeAddOp2(v, OP_ResultRow, 1, 1);
+    goto cleanup;
+  }
+
+  sqlite3OsFileSize(fd, &file_sz);
+  hmac_out = sqlcipher_malloc(ctx->hmac_sz);
+
+  for(page = 1; page <= file_sz / ctx->page_sz; page++) {
+    int offset = (page - 1) * ctx->page_sz;
+    int payload_sz = ctx->page_sz - ctx->reserve_sz + ctx->iv_sz;
+    int read_sz = ctx->page_sz;
+
+    if(page==1) {
+      int page1_offset = ctx->plaintext_header_sz ? ctx->plaintext_header_sz : FILE_HEADER_SZ;
+      read_sz = read_sz - page1_offset;
+      payload_sz = payload_sz - page1_offset;
+      offset += page1_offset;
+    }
+
+    sqlcipher_memset(ctx->buffer, 0, ctx->page_sz);
+    sqlcipher_memset(hmac_out, 0, ctx->hmac_sz);
+    if(sqlite3OsRead(fd, ctx->buffer, read_sz, offset) != SQLITE_OK) {
+      result = sqlite3_mprintf("error reading %d bytes from file page %d at offset %d\n", read_sz, page, offset);
+      sqlite3VdbeAddOp4(v, OP_String8, 0, 1, 0, result, P4_DYNAMIC);
+      sqlite3VdbeAddOp2(v, OP_ResultRow, 1, 1);
+    } else if(sqlcipher_page_hmac(ctx, ctx->read_ctx, page, ctx->buffer, payload_sz, hmac_out) != SQLITE_OK) {
+      result = sqlite3_mprintf("HMAC operation failed for page %d", page);
+      sqlite3VdbeAddOp4(v, OP_String8, 0, 1, 0, result, P4_DYNAMIC);
+      sqlite3VdbeAddOp2(v, OP_ResultRow, 1, 1);
+    } else if(sqlcipher_memcmp(ctx->buffer + payload_sz, hmac_out, ctx->hmac_sz) != 0) {
+      result = sqlite3_mprintf("HMAC verification failed for page %d", page);
+      sqlite3VdbeAddOp4(v, OP_String8, 0, 1, 0, result, P4_DYNAMIC);
+      sqlite3VdbeAddOp2(v, OP_ResultRow, 1, 1);
+    }
+  }
+
+  if(file_sz % ctx->page_sz != 0) {
+    result = sqlite3_mprintf("page %d has an invalid size of %d bytes", page, file_sz - ((file_sz / ctx->page_sz) * ctx->page_sz));
+    sqlite3VdbeAddOp4(v, OP_String8, 0, 1, 0, result, P4_DYNAMIC);
+    sqlite3VdbeAddOp2(v, OP_ResultRow, 1, 1);
+  }
+
+cleanup:
+  if(trans_rc == SQLITE_OK) sqlite3BtreeRollback(ctx->pBt, SQLITE_OK, 0);
+  if(hmac_out != NULL) sqlcipher_free(hmac_out, ctx->hmac_sz);
+  return SQLITE_OK;
+}
+
 int sqlcipher_codec_ctx_migrate(codec_ctx *ctx) {
   int i, pass_sz, keyspec_sz, nRes, user_version, rc, oflags;
   Db *pDb = 0;
diff --git a/test/sqlcipher-core.test b/test/sqlcipher-core.test
@@ -531,84 +531,6 @@ do_test custom-pagesize-must-match {
 db close
 file delete -force test.db
 
-# 1. create a database and insert a bunch of data, close the database
-# 2. seek to the middle of a database page and write some junk
-# 3. Open the database and verify that the database is no longer readable
-do_test hmac-tamper-resistence {
-  sqlite_orig db test.db
-
-  execsql {
-    PRAGMA key = 'testkey';
-    CREATE table t1(a,b);
-    BEGIN;
-  }
-
-  for {set i 1} {$i<=1000} {incr i} {
-    set r [expr {int(rand()*500000)}]
-    execsql "INSERT INTO t1 VALUES($i,'value $r');" 
-  }
-
-  execsql {
-    COMMIT;
-  } 
-
-  db close
-
-  # write some junk into the hmac segment, leaving
-  # the page data valid but with an invalid signature
-  hexio_write test.db 1000 0000
-
-  sqlite_orig db test.db
-
-  catchsql {
-    PRAGMA key = 'testkey';
-    SELECT count(*) FROM t1;
-  }
-
-} {1 {file is not a database}}
-db close
-file delete -force test.db
-
-# 1. create a database and insert a bunch of data, close the database
-# 2. seek to the middle of a database page and write some junk
-# 3. Open the database and verify that the database is still readable
-do_test nohmac-not-tamper-resistent {
-  sqlite_orig db test.db
-
-  execsql {
-    PRAGMA key = 'testkey';
-    PRAGMA cipher_use_hmac = OFF;
-    PRAGMA cipher_page_size = 1024;
-    CREATE table t1(a,b);
-    BEGIN;
-  }
-
-  for {set i 1} {$i<=1000} {incr i} {
-    set r [expr {int(rand()*500000)}]
-    execsql "INSERT INTO t1 VALUES($i,'value $r');" 
-  }
-
-  execsql {
-    COMMIT;
-  } 
-
-  db close
-
-  # write some junk into the middle of the page
-  hexio_write test.db 2560 00
-
-  sqlite_orig db test.db
-
-  execsql {
-    PRAGMA key = 'testkey';
-    PRAGMA cipher_use_hmac = OFF;
-    PRAGMA cipher_page_size = 1024;
-    SELECT count(*) FROM t1;
-  }
-
-} {1000}
-db close
-file delete -force test.db
 
 # 1. create a database with WAL journal mode
 # 2. create table and insert operations should work
diff --git a/test/sqlcipher-integrity.test b/test/sqlcipher-integrity.test
diff --git a/test/sqlcipher.test b/test/sqlcipher.test

Original file line number	Diff line number	Diff line change
`@@ -629,6 +629,11 @@ int sqlcipher_codec_pragma(sqlite3* db, int iDb, Parse pParse, const char zLef`
`629`	`629`	`pragma = sqlite3_mprintf("PRAGMA cipher_default_kdf_algorithm = %s;", SQLCIPHER_PBKDF2_HMAC_SHA512_LABEL);`
`630`	`630`	`}`
`631`	`631`	`codec_vdbe_return_string(pParse, "pragma", pragma, P4_DYNAMIC);`
	`632`	`+ }else`
	`633`	`+ if( sqlite3StrICmp(zLeft,"cipher_integrity_check")==0 ){`
	`634`	`+ if(ctx) {`
	`635`	`+ sqlcipher_codec_ctx_integrity_check(ctx, pParse, "cipher_integrity_check");`
	`636`	`+ }`
`632`	`637`	`}else {`
`633`	`638`	`return 0;`
`634`	`639`	`}`