/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ /* vim: set ts=8 sts=2 et sw=2 tw=80: */ /* This Source Code Form is subject to the terms of the Mozilla Public * License, v. 2.0. If a copy of the MPL was not distributed with this * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ #include "CTObjectsExtractor.h" #include "hasht.h" #include "mozilla/Assertions.h" #include "mozilla/Casting.h" #include "mozilla/Move.h" #include "mozilla/PodOperations.h" #include "mozilla/RangedPtr.h" #include "mozilla/Vector.h" #include "pkix/pkixnss.h" #include "pkixutil.h" namespace mozilla { namespace ct { using namespace mozilla::pkix; // Holds a non-owning pointer to a byte buffer and allows writing chunks of data // to the buffer, placing the later chunks after the earlier ones // in a stream-like fashion. // Note that writing to Output always succeeds. If the internal buffer // overflows, an error flag is turned on and you won't be able to retrieve // the final data. class Output { public: Output(uint8_t* buffer, size_t length) : begin(buffer) , end(buffer + length) , current(buffer, begin, end) , overflowed(false) { } template <size_t N> explicit Output(uint8_t (&buffer)[N]) : Output(buffer, N) { } void Write(Input data) { Write(data.UnsafeGetData(), data.GetLength()); } void Write(uint8_t b) { Write(&b, 1); } bool IsOverflowed() const { return overflowed; } Result GetInput(/*out*/ Input& input) const { if (overflowed) { return Result::FATAL_ERROR_INVALID_STATE; } size_t length = AssertedCast<size_t>(current.get() - begin); return input.Init(begin, length); } private: uint8_t* begin; uint8_t* end; RangedPtr<uint8_t> current; bool overflowed; Output(const Output&) = delete; void operator=(const Output&) = delete; void Write(const uint8_t* data, size_t length) { size_t available = AssertedCast<size_t>(end - current.get()); if (available < length) { overflowed = true; } if (overflowed) { return; } PodCopy(current.get(), data, length); current += length; } }; // For reference: // // Certificate ::= SEQUENCE { // tbsCertificate TBSCertificate, // signatureAlgorithm AlgorithmIdentifier, // signatureValue BIT STRING } // // TBSCertificate ::= SEQUENCE { // version [0] EXPLICIT Version DEFAULT v1, // serialNumber CertificateSerialNumber, // signature AlgorithmIdentifier, // issuer Name, // validity Validity, // subject Name, // subjectPublicKeyInfo SubjectPublicKeyInfo, // issuerUniqueID [1] IMPLICIT UniqueIdentifier OPTIONAL, // -- If present, version MUST be v2 or v3 // subjectUniqueID [2] IMPLICIT UniqueIdentifier OPTIONAL, // -- If present, version MUST be v2 or v3 // extensions [3] EXPLICIT Extensions OPTIONAL // -- If present, version MUST be v3 // } // python DottedOIDToCode.py id-embeddedSctList 1.3.6.1.4.1.11129.2.4.2 // See Section 3.3 of RFC 6962. static const uint8_t EMBEDDED_SCT_LIST_OID[] = { 0x2b, 0x06, 0x01, 0x04, 0x01, 0xd6, 0x79, 0x02, 0x04, 0x02 }; // Maximum length of DER TLV header static const size_t MAX_TLV_HEADER_LENGTH = 4; // DER tag of the "extensions [3]" field from TBSCertificate static const uint8_t EXTENSIONS_CONTEXT_TAG = der::CONTEXT_SPECIFIC | der::CONSTRUCTED | 3; // Given a leaf certificate, extracts the DER-encoded TBSCertificate component // of the corresponding Precertificate. // Basically, the extractor needs to remove the embedded SCTs extension // from the certificate and return its TBSCertificate. We do it in an ad hoc // manner by breaking the source DER into several parts and then joining // the right parts, taking care to update the relevant TLV headers. // See WriteOutput for more details on the parts involved. class PrecertTBSExtractor { public: // |buffer| is the buffer to be used for writing the output. Since the // required buffer size is not generally known in advance, it's best // to use at least the size of the input certificate DER. PrecertTBSExtractor(Input der, uint8_t* buffer, size_t bufferLength) : mDER(der) , mOutput(buffer, bufferLength) { } // Performs the extraction. Result Init() { Reader tbsReader; Result rv = GetTBSCertificate(tbsReader); if (rv != Success) { return rv; } rv = ExtractTLVsBeforeExtensions(tbsReader); if (rv != Success) { return rv; } rv = ExtractOptionalExtensionsExceptSCTs(tbsReader); if (rv != Success) { return rv; } return WriteOutput(); } // Use to retrieve the result after a successful call to Init. // The returned Input points to the buffer supplied in the constructor. Input GetPrecertTBS() { return mPrecertTBS; } private: Result GetTBSCertificate(Reader& tbsReader) { Reader certificateReader; Result rv = der::ExpectTagAndGetValueAtEnd(mDER, der::SEQUENCE, certificateReader); if (rv != Success) { return rv; } return ExpectTagAndGetValue(certificateReader, der::SEQUENCE, tbsReader); } Result ExtractTLVsBeforeExtensions(Reader& tbsReader) { Reader::Mark tbsBegin = tbsReader.GetMark(); while (!tbsReader.AtEnd()) { if (tbsReader.Peek(EXTENSIONS_CONTEXT_TAG)) { break; } uint8_t tag; Input tagValue; Result rv = der::ReadTagAndGetValue(tbsReader, tag, tagValue); if (rv != Success) { return rv; } } return tbsReader.GetInput(tbsBegin, mTLVsBeforeExtensions); } Result ExtractOptionalExtensionsExceptSCTs(Reader& tbsReader) { if (!tbsReader.Peek(EXTENSIONS_CONTEXT_TAG)) { return Success; } Reader extensionsContextReader; Result rv = der::ExpectTagAndGetValueAtEnd(tbsReader, EXTENSIONS_CONTEXT_TAG, extensionsContextReader); if (rv != Success) { return rv; } Reader extensionsReader; rv = der::ExpectTagAndGetValueAtEnd(extensionsContextReader, der::SEQUENCE, extensionsReader); if (rv != Success) { return rv; } while (!extensionsReader.AtEnd()) { Reader::Mark extensionTLVBegin = extensionsReader.GetMark(); Reader extension; rv = der::ExpectTagAndGetValue(extensionsReader, der::SEQUENCE, extension); if (rv != Success) { return rv; } Reader extensionID; rv = der::ExpectTagAndGetValue(extension, der::OIDTag, extensionID); if (rv != Success) { return rv; } if (!extensionID.MatchRest(EMBEDDED_SCT_LIST_OID)) { Input extensionTLV; rv = extensionsReader.GetInput(extensionTLVBegin, extensionTLV); if (rv != Success) { return rv; } if (!mExtensionTLVs.append(Move(extensionTLV))) { return Result::FATAL_ERROR_NO_MEMORY; } } } return Success; } Result WriteOutput() { // What should be written here: // // TBSCertificate ::= SEQUENCE (TLV with header |tbsHeader|) // dump of |mTLVsBeforeExtensions| // extensions [3] OPTIONAL (TLV with header |extensionsContextHeader|) // SEQUENCE (TLV with with header |extensionsHeader|) // dump of |mExtensionTLVs| Result rv; if (mExtensionTLVs.length() > 0) { uint8_t tbsHeaderBuffer[MAX_TLV_HEADER_LENGTH]; uint8_t extensionsContextHeaderBuffer[MAX_TLV_HEADER_LENGTH]; uint8_t extensionsHeaderBuffer[MAX_TLV_HEADER_LENGTH]; Input tbsHeader; Input extensionsContextHeader; Input extensionsHeader; // Count the total size of the extensions. Note that since // the extensions data is contained within mDER (an Input), // their combined length won't overflow Input::size_type. Input::size_type extensionsValueLength = 0; for (auto& extensionTLV : mExtensionTLVs) { extensionsValueLength += extensionTLV.GetLength(); } rv = MakeTLVHeader(der::SEQUENCE, extensionsValueLength, extensionsHeaderBuffer, extensionsHeader); if (rv != Success) { return rv; } Input::size_type extensionsContextLength = AssertedCast<Input::size_type>(extensionsHeader.GetLength() + extensionsValueLength); rv = MakeTLVHeader(EXTENSIONS_CONTEXT_TAG, extensionsContextLength, extensionsContextHeaderBuffer, extensionsContextHeader); if (rv != Success) { return rv; } Input::size_type tbsLength = AssertedCast<Input::size_type>(mTLVsBeforeExtensions.GetLength() + extensionsContextHeader.GetLength() + extensionsHeader.GetLength() + extensionsValueLength); rv = MakeTLVHeader(der::SEQUENCE, tbsLength, tbsHeaderBuffer, tbsHeader); if (rv != Success) { return rv; } mOutput.Write(tbsHeader); mOutput.Write(mTLVsBeforeExtensions); mOutput.Write(extensionsContextHeader); mOutput.Write(extensionsHeader); for (auto& extensionTLV : mExtensionTLVs) { mOutput.Write(extensionTLV); } } else { uint8_t tbsHeaderBuffer[MAX_TLV_HEADER_LENGTH]; Input tbsHeader; rv = MakeTLVHeader(der::SEQUENCE, mTLVsBeforeExtensions.GetLength(), tbsHeaderBuffer, tbsHeader); if (rv != Success) { return rv; } mOutput.Write(tbsHeader); mOutput.Write(mTLVsBeforeExtensions); } return mOutput.GetInput(mPrecertTBS); } Result MakeTLVHeader(uint8_t tag, size_t length, uint8_t (&buffer)[MAX_TLV_HEADER_LENGTH], /*out*/ Input& header) { Output output(buffer); output.Write(tag); if (length < 128) { output.Write(AssertedCast<uint8_t>(length)); } else if (length < 256) { output.Write(0x81u); output.Write(AssertedCast<uint8_t>(length)); } else if (length < 65536) { output.Write(0x82u); output.Write(AssertedCast<uint8_t>(length / 256)); output.Write(AssertedCast<uint8_t>(length % 256)); } else { return Result::FATAL_ERROR_INVALID_ARGS; } return output.GetInput(header); } Input mDER; Input mTLVsBeforeExtensions; Vector<Input, 16> mExtensionTLVs; Output mOutput; Input mPrecertTBS; }; Result GetPrecertLogEntry(Input leafCertificate, Input issuerSubjectPublicKeyInfo, LogEntry& output) { MOZ_ASSERT(leafCertificate.GetLength() > 0); MOZ_ASSERT(issuerSubjectPublicKeyInfo.GetLength() > 0); output.Reset(); Buffer precertTBSBuffer; if (!precertTBSBuffer.resize(leafCertificate.GetLength())) { return Result::FATAL_ERROR_NO_MEMORY; } PrecertTBSExtractor extractor(leafCertificate, precertTBSBuffer.begin(), precertTBSBuffer.length()); Result rv = extractor.Init(); if (rv != Success) { return rv; } Input precertTBS(extractor.GetPrecertTBS()); MOZ_ASSERT(precertTBS.UnsafeGetData() == precertTBSBuffer.begin()); precertTBSBuffer.shrinkTo(precertTBS.GetLength()); output.type = LogEntry::Type::Precert; output.tbsCertificate = Move(precertTBSBuffer); if (!output.issuerKeyHash.resizeUninitialized(SHA256_LENGTH)) { return Result::FATAL_ERROR_NO_MEMORY; } return DigestBufNSS(issuerSubjectPublicKeyInfo, DigestAlgorithm::sha256, output.issuerKeyHash.begin(), output.issuerKeyHash.length()); } Result GetX509LogEntry(Input leafCertificate, LogEntry& output) { MOZ_ASSERT(leafCertificate.GetLength() > 0); output.Reset(); output.type = LogEntry::Type::X509; return InputToBuffer(leafCertificate, output.leafCertificate); } } } // namespace mozilla::ct