pitrou commented on code in PR #48859:
URL: https://github.com/apache/arrow/pull/48859#discussion_r2707611800
##########
cpp/src/parquet/metadata.cc:
##########
@@ -834,6 +834,43 @@ class FileMetaData::FileMetaDataImpl {
tag, encryption::kGcmTagLength);
}
+ bool VerifySignature(std::span<const uint8_t> serialized_metadata,
+ std::span<const uint8_t> signature) {
+ // Verify decryption properties are set
+ if (file_decryptor_ == nullptr) {
+ throw ParquetException("Decryption not set properly. cannot verify
signature");
+ }
+
+ if (signature.size() != encryption::kGcmTagLength +
encryption::kNonceLength) {
+ throw ParquetInvalidOrCorruptedFileException(
+ "Invalid footer encryption signature (expected ",
+ encryption::kGcmTagLength + encryption::kNonceLength, " bytes, got ",
+ signature.size(), ")");
+ }
+
+ // Encrypt plaintext serialized metadata so as to compute its signature
+ auto nonce = signature.subspan(0, encryption::kNonceLength);
+ auto tag = signature.subspan(encryption::kNonceLength);
+ const SecureString& key = file_decryptor_->GetFooterKey();
+ const std::string& aad =
encryption::CreateFooterAad(file_decryptor_->file_aad());
+
+ auto aes_encryptor =
encryption::AesEncryptor::Make(file_decryptor_->algorithm(),
+
static_cast<int>(key.size()),
+ true, false
/*write_length*/);
+
+ std::shared_ptr<Buffer> encrypted_buffer =
+ AllocateBuffer(file_decryptor_->pool(),
+
aes_encryptor->CiphertextLength(serialized_metadata.size()));
+ int32_t encrypted_len = aes_encryptor->SignedFooterEncrypt(
Review Comment:
To quote [the spec about plaintext
footers](https://github.com/apache/parquet-format/blob/master/Encryption.md#55-plaintext-footer-mode):
> The footer signing is done by encrypting the serialized FileMetaData
structure with the AES GCM algorithm - using a footer signing key, and an AAD
constructed according to the instructions of the section 4.4. Only the nonce
and GCM tag are stored in the file – as a 28-byte fixed-length array, written
right after the footer itself.
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