GH-41246: [Docs][C++][Python] Improve docs on column encryption for nested fields

cpp/examples/arrow/CMakeLists.txt

@@ -166,6 +166,15 @@ if(ARROW_PARQUET AND ARROW_DATASET)
                     ${DATASET_EXAMPLES_LINK_LIBS})
   add_dependencies(execution-plan-documentation-examples parquet)
 
+  if(PARQUET_REQUIRE_ENCRYPTION)
+    add_arrow_example(parquet_column_encryption
+                      EXTRA_SOURCES
+                      ${PROJECT_SOURCE_DIR}/src/parquet/encryption/test_in_memory_kms.cc
+                      EXTRA_LINK_LIBS
+                      ${DATASET_EXAMPLES_LINK_LIBS})
+    add_dependencies(parquet-column-encryption parquet)
+  endif()
+
   if(ARROW_CSV)
     add_arrow_example(join_example EXTRA_LINK_LIBS ${DATASET_EXAMPLES_LINK_LIBS})
     add_dependencies(join-example parquet)

cpp/examples/arrow/parquet_column_encryption.cc

@@ -0,0 +1,239 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include <arrow/util/logging.h>
+
+#include "arrow/dataset/file_parquet.h"
+#include "arrow/dataset/parquet_encryption_config.h"
+#include "arrow/filesystem//localfs.h"
+#include "parquet/encryption/crypto_factory.h"
+#include "parquet/encryption/test_in_memory_kms.h"
+
+#include "arrow/api.h"
+#include "arrow/result.h"
+#include "parquet/arrow/reader.h"
+
+#include <arrow/filesystem/path_util.h>
+#include <iostream>
+#include <utility>
+
+namespace fs = arrow::fs;
+
+namespace ds = arrow::dataset;
+
+arrow::Result<std::shared_ptr<arrow::Table>> GetTable() {
+  auto int_builder = arrow::Int32Builder();
+
+  std::shared_ptr<arrow::Array> arr_i;
+  ARROW_RETURN_NOT_OK(int_builder.AppendValues({1, 3, 5, 7, 1}));
+  ARROW_RETURN_NOT_OK(int_builder.Finish(&arr_i));
+
+  auto struct_type = arrow::struct_({{"a", arrow::int32()}, {"b", arrow::int64()}});
+  auto pool = arrow::default_memory_pool();
+  auto a_builder = std::make_shared<arrow::Int32Builder>();
+  auto b_builder = std::make_shared<arrow::Int64Builder>();
+  auto struct_builder = arrow::StructBuilder(struct_type, pool, {a_builder, b_builder});
+
+  std::shared_ptr<arrow::Array> arr_struct;
+  ARROW_RETURN_NOT_OK(struct_builder.Append());
+  ARROW_RETURN_NOT_OK(a_builder->Append(2));
+  ARROW_RETURN_NOT_OK(b_builder->Append(20));
+  ARROW_RETURN_NOT_OK(struct_builder.Append());
+  ARROW_RETURN_NOT_OK(a_builder->Append(4));
+  ARROW_RETURN_NOT_OK(b_builder->Append(40));
+  ARROW_RETURN_NOT_OK(struct_builder.Append());
+  ARROW_RETURN_NOT_OK(a_builder->Append(6));
+  ARROW_RETURN_NOT_OK(b_builder->Append(60));
+  ARROW_RETURN_NOT_OK(struct_builder.Append());
+  ARROW_RETURN_NOT_OK(a_builder->Append(8));
+  ARROW_RETURN_NOT_OK(b_builder->Append(80));
+  ARROW_RETURN_NOT_OK(struct_builder.Append());
+  ARROW_RETURN_NOT_OK(a_builder->Append(10));
+  ARROW_RETURN_NOT_OK(b_builder->Append(100));
+  ARROW_RETURN_NOT_OK(struct_builder.Finish(&arr_struct));
+
+  auto map_type = arrow::map(arrow::int32(), arrow::utf8());
+  auto key_builder = std::make_shared<arrow::Int32Builder>();
+  auto item_builder = std::make_shared<arrow::StringBuilder>();
+  auto map_builder = arrow::MapBuilder(pool, key_builder, item_builder, map_type);
+
+  std::shared_ptr<arrow::Array> arr_map;
+  ARROW_RETURN_NOT_OK(map_builder.Append());
+  ARROW_RETURN_NOT_OK(key_builder->AppendValues({2, 4}));
+  ARROW_RETURN_NOT_OK(item_builder->AppendValues({"2", "4"}));
+  ARROW_RETURN_NOT_OK(map_builder.Append());
+  ARROW_RETURN_NOT_OK(key_builder->AppendValues({6}));
+  ARROW_RETURN_NOT_OK(item_builder->AppendValues({"6"}));
+  ARROW_RETURN_NOT_OK(map_builder.Append());
+  ARROW_RETURN_NOT_OK(map_builder.Append());
+  ARROW_RETURN_NOT_OK(key_builder->AppendValues({8, 10}));
+  ARROW_RETURN_NOT_OK(item_builder->AppendValues({"8", "10"}));
+  ARROW_RETURN_NOT_OK(map_builder.Append());
+  ARROW_RETURN_NOT_OK(map_builder.Finish(&arr_map));
+
+  auto list_type = arrow::list(arrow::int32());
+  auto value_builder = std::make_shared<arrow::Int32Builder>();
+  auto list_builder = arrow::ListBuilder(pool, value_builder, list_type);
+
+  std::shared_ptr<arrow::Array> arr_list;
+  ARROW_RETURN_NOT_OK(list_builder.Append());
+  ARROW_RETURN_NOT_OK(value_builder->AppendValues({1, 2, 3}));
+  ARROW_RETURN_NOT_OK(list_builder.Append());
+  ARROW_RETURN_NOT_OK(value_builder->AppendValues({4, 5, 6}));
+  ARROW_RETURN_NOT_OK(list_builder.Append());
+  ARROW_RETURN_NOT_OK(value_builder->AppendValues({7}));
+  ARROW_RETURN_NOT_OK(list_builder.Append());
+  ARROW_RETURN_NOT_OK(value_builder->AppendValues({8}));
+  ARROW_RETURN_NOT_OK(list_builder.Append());
+  ARROW_RETURN_NOT_OK(list_builder.Finish(&arr_list));
+
+  auto schema = arrow::schema({
+      arrow::field("i", arrow::int32()),
+      arrow::field("s", struct_type),
+      arrow::field("m", map_type),
+      arrow::field("l", list_type),
+  });
+
+  return arrow::Table::Make(schema, {arr_i, arr_struct, arr_map, arr_list});
+}
+
+std::shared_ptr<parquet::encryption::CryptoFactory> GetCryptoFactory() {
+  // Configure KMS.
+  std::unordered_map<std::string, std::string> key_map;
+  key_map.emplace("footerKeyId", "0123456789012345");
+  key_map.emplace("columnKeyId", "1234567890123456");
+
+  auto crypto_factory = std::make_shared<parquet::encryption::CryptoFactory>();
+  auto kms_client_factory =
+      // for testing only, do not use it as an example of KmsClientFactory implementation
+      std::make_shared<parquet::encryption::TestOnlyInMemoryKmsClientFactory>(
+          /*wrap_locally=*/true, key_map);
+  crypto_factory->RegisterKmsClientFactory(std::move(kms_client_factory));
+  return crypto_factory;
+}
+
+arrow::Status WriteEncryptedFile(const std::string& path_to_file) {
+  using arrow::internal::checked_pointer_cast;
+
+  // Get a configured crypto factory and kms connection conf.
+  auto crypto_factory = GetCryptoFactory();
+  auto kms_connection_config =
+      std::make_shared<parquet::encryption::KmsConnectionConfig>();
+
+  // Set write options with encryption configuration.
+  auto encryption_config = std::make_shared<parquet::encryption::EncryptionConfiguration>(
+      std::string("footerKeyId"));
+  encryption_config->column_keys =
+      "columnKeyId: i, s.a, s.b, m.key_value.key, m.key_value.value, l.list.element";
+
+  auto parquet_encryption_config = std::make_shared<ds::ParquetEncryptionConfig>();
+  // Directly assign shared_ptr objects to ParquetEncryptionConfig members.
+  parquet_encryption_config->crypto_factory = crypto_factory;
+  parquet_encryption_config->kms_connection_config = kms_connection_config;
+  parquet_encryption_config->encryption_config = std::move(encryption_config);
+
+  auto file_format = std::make_shared<ds::ParquetFileFormat>();
+  auto parquet_file_write_options = checked_pointer_cast<ds::ParquetFileWriteOptions>(
+      file_format->DefaultWriteOptions());
+  parquet_file_write_options->parquet_encryption_config =
+      std::move(parquet_encryption_config);
+
+  // Write dataset.
+  ARROW_ASSIGN_OR_RAISE(std::shared_ptr<arrow::Table> table, GetTable());
+  printf("%s", table->ToString().c_str());
+  auto dataset = std::make_shared<ds::InMemoryDataset>(table);
+  ARROW_ASSIGN_OR_RAISE(auto scanner_builder, dataset->NewScan());
+  ARROW_ASSIGN_OR_RAISE(auto scanner, scanner_builder->Finish());
+
+  auto file_system = std::make_shared<fs::LocalFileSystem>();
+  auto partitioning = std::make_shared<ds::HivePartitioning>(
+      arrow::schema({arrow::field("part", arrow::utf8())}));
+
+  ds::FileSystemDatasetWriteOptions write_options;
+  write_options.file_write_options = parquet_file_write_options;
+  write_options.filesystem = file_system;
+  write_options.base_dir = path_to_file;
+  write_options.partitioning = partitioning;
+  write_options.basename_template = "part{i}.parquet";
+  ARROW_CHECK_OK(ds::FileSystemDataset::Write(write_options, std::move(scanner)));
+  return arrow::Status::OK();
+}
+
+arrow::Status ReadEncryptedFile(const std::string& path_to_file) {
+  // Get a configured crypto factory and kms connection conf
+  auto crypto_factory = GetCryptoFactory();
+  auto kms_connection_config =
+      std::make_shared<parquet::encryption::KmsConnectionConfig>();
+
+  // Create decryption properties.
+  auto decryption_config =
+      std::make_shared<parquet::encryption::DecryptionConfiguration>();
+  auto parquet_decryption_config = std::make_shared<ds::ParquetDecryptionConfig>();
+  parquet_decryption_config->crypto_factory = crypto_factory;
+  parquet_decryption_config->kms_connection_config = kms_connection_config;
+  parquet_decryption_config->decryption_config = std::move(decryption_config);
+
+  // Set scan options.
+  auto parquet_scan_options = std::make_shared<ds::ParquetFragmentScanOptions>();
+  parquet_scan_options->parquet_decryption_config = std::move(parquet_decryption_config);
+
+  // Get configured Parquet file format
+  auto file_format = std::make_shared<ds::ParquetFileFormat>();
+  file_format->default_fragment_scan_options = std::move(parquet_scan_options);
+
+  // Get the FileSystem.
+  auto file_system = std::make_shared<fs::LocalFileSystem>();
+
+  // Get FileInfo objects for all files under the base directory
+  fs::FileSelector selector;
+  selector.base_dir = path_to_file;
+  selector.recursive = true;
+
+  // Create the dataset
+  ds::FileSystemFactoryOptions factory_options;
+  ARROW_ASSIGN_OR_RAISE(auto dataset_factory,
+                        ds::FileSystemDatasetFactory::Make(file_system, selector,
+                                                           file_format, factory_options));
+  ARROW_ASSIGN_OR_RAISE(auto dataset, dataset_factory->Finish());
+  ARROW_ASSIGN_OR_RAISE(auto scanner_builder, dataset->NewScan());
+  ARROW_ASSIGN_OR_RAISE(auto scanner, scanner_builder->Finish());
+  ARROW_ASSIGN_OR_RAISE(auto table, scanner->ToTable());
+  std::cout << "Table size: " << table->num_rows() << "\n";
+  return arrow::Status::OK();
+}
+
+arrow::Status RunExamples(const std::string& path_to_file) {
+  ARROW_RETURN_NOT_OK(WriteEncryptedFile(path_to_file));
+  ARROW_RETURN_NOT_OK(ReadEncryptedFile(path_to_file));
+  return arrow::Status::OK();
+}
+
+int main(int argc, char** argv) {
+  if (argc != 2) {
+    // Fake success for CI purposes.
+    return EXIT_SUCCESS;
+  }
+
+  std::string path_to_file = argv[1];
+  arrow::Status status = RunExamples(path_to_file);
+
+  if (!status.ok()) {
+    std::cerr << "Error occurred: " << status.message() << std::endl;
+    return EXIT_FAILURE;
+  }
+  return EXIT_SUCCESS;
+}

cpp/examples/arrow/parquet_read_write.cc

@@ -165,7 +165,7 @@ arrow::Status WriteInBatches(std::string path_to_file) {
   return arrow::Status::OK();
 }
 
-arrow::Status RunExamples(std::string path_to_file) {
+arrow::Status RunExamples(const std::string& path_to_file) {
   ARROW_RETURN_NOT_OK(WriteFullFile(path_to_file));
   ARROW_RETURN_NOT_OK(ReadFullFile(path_to_file));
   ARROW_RETURN_NOT_OK(WriteInBatches(path_to_file));

cpp/src/parquet/encryption/crypto_factory.h

@@ -43,8 +43,8 @@ struct PARQUET_EXPORT EncryptionConfiguration {
   /// ID of the master key for footer encryption/signing
   std::string footer_key;
 
-  /// List of columns to encrypt, with master key IDs (see HIVE-21848).
-  /// Format: "masterKeyID:colName,colName;masterKeyID:colName..."
+  /// List of columns to encrypt, with column master key IDs (see HIVE-21848).
+  /// Format: "columnKeyID:colName,colName;columnKeyID:colName..."
   /// Either
   /// (1) column_keys must be set
   /// or

docs/source/cpp/dataset.rst

@@ -445,8 +445,6 @@ storage systems, such as Amazon S3, by passing a different filesystem.
 See the :ref:`filesystem <cpp-filesystems>` docs for more details on the available
 filesystems.
 
-.. _cpp-dataset-full-example:
-
 A note on transactions & ACID guarantees
 ----------------------------------------
 
@@ -467,6 +465,8 @@ Most file formats have magic numbers which are written at the end.  This means a
 partial file write can safely be detected and discarded.  The CSV file format does
 not have any such concept and a partially written CSV file may be detected as valid.
 
+.. _cpp-dataset-full-example:
+
 Full Example
 ------------
 

docs/source/cpp/examples/index.rst

@@ -25,6 +25,7 @@ Examples
    compute_and_write_example
    dataset_documentation_example
    dataset_skyhook_scan_example
+   parquet_column_encryption
    row_columnar_conversion
    std::tuple-like ranges to Arrow <tuple_range_conversion>
    Converting RecordBatch to Tensor <converting_recordbatch_to_tensor>

docs/source/cpp/examples/parquet_column_encryption.rst

@@ -0,0 +1,29 @@
+.. Licensed to the Apache Software Foundation (ASF) under one
+.. or more contributor license agreements.  See the NOTICE file
+.. distributed with this work for additional information
+.. regarding copyright ownership.  The ASF licenses this file
+.. to you under the Apache License, Version 2.0 (the
+.. "License"); you may not use this file except in compliance
+.. with the License.  You may obtain a copy of the License at
+
+..   http://www.apache.org/licenses/LICENSE-2.0
+
+.. Unless required by applicable law or agreed to in writing,
+.. software distributed under the License is distributed on an
+.. "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+.. KIND, either express or implied.  See the License for the
+.. specific language governing permissions and limitations
+.. under the License.
+
+.. default-domain:: cpp
+.. highlight:: cpp
+
+Parquet column encryption
+=========================
+
+The following example defines a :class:`arrow::Table` instance, and then writes
+it to an encrypted Parquet file. Metadata footer and columns are encrypted with
+different encryption keys.
+
+.. literalinclude:: ../../../../cpp/examples/arrow/parquet_column_encryption.cc
+

docs/source/cpp/parquet.rst

@@ -585,6 +585,51 @@ More specifically, Parquet C++ supports:
 * EncryptionWithFooterKey and EncryptionWithColumnKey modes.
 * Encrypted Footer and Plaintext Footer modes.
 
+Configuration
+~~~~~~~~~~~~~
+
+Parquet encryption uses a ``parquet::encryption::CryptoFactory`` that has access to a
+Key Management System (KMS), which stores actual encryption keys, referenced by key ids.
+The Parquet encryption configuration only uses key ids, no actual keys.
+
+Parquet metadata encryption is configured via ``parquet::encryption::EncryptionConfiguration``:
+
+.. literalinclude:: ../../../cpp/examples/arrow/parquet_column_encryption.cc
+   :language: cpp
+   :start-at: // Set write options with encryption configuration
+   :end-before: encryption_config->column_keys
+   :dedent: 2
+
+All columns are encrypted with the same key as the Parquet metadata when above
+``encryption_config->uniform_encryption`` is set ``true``.
+
+Individual columns are encrypted with individual keys as configured via ``encryption_config->column_keys``.
+This field expects a string of the format ``"columnKeyID:colName,colName;columnKeyID:colName..."``.
+
+.. literalinclude:: ../../../cpp/examples/arrow/parquet_column_encryption.cc
+   :language: cpp
+   :start-at: // Set write options with encryption configuration
+   :end-before: auto parquet_encryption_config
+   :emphasize-lines: 4-5
+   :dedent: 2
+
+See the full `Parquet column encryption example <examples/parquet_column_encryption.html>`_.
+
+.. note::
+
+   Encrypting columns that have nested fields (struct, map, or even list data types)
+   requires column keys for the inner fields, not the column itself.
+   Configuring a column key for the column itself causes this error (here column name is ``col``):
+
+   .. code-block::
+
+      OSError: Encrypted column col not in file schema
+
+   The key and value fields of a map column ``m`` has the names ``m.key_value.key``
+   and  ``m.key_value.value``, respectively. The inner field of a list column ``l``
+   has the name ``l.list.element``. An inner field ``f`` of a struct column ``s`` has
+   the name ``s.f``.
+
 Miscellaneous
 -------------