pki/verify_name_match.cc - boringssl - Git at Google

 // Copyright 2015 The Chromium Authors
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include "verify_name_match.h"

 #include "cert_error_params.h"
 #include "cert_errors.h"
 #include "parse_name.h"
 #include "input.h"
 #include "parser.h"
 #include "tag.h"
 #include <openssl/bytestring.h>

 namespace bssl {

 DEFINE_CERT_ERROR_ID(kFailedConvertingAttributeValue,
                      "Failed converting AttributeValue to string");
 DEFINE_CERT_ERROR_ID(kFailedNormalizingString, "Failed normalizing string");

 namespace {

 // Types of character set checking that NormalizeDirectoryString can perform.
 enum CharsetEnforcement {
   NO_ENFORCEMENT,
   ENFORCE_PRINTABLE_STRING,
   ENFORCE_ASCII,
 };

 // Normalizes |output|, a UTF-8 encoded string, as if it contained
 // only ASCII characters.
 //
 // This could be considered a partial subset of RFC 5280 rules, and
 // is compatible with RFC 2459/3280.
 //
 // In particular, RFC 5280, Section 7.1 describes how UTF8String
 // and PrintableString should be compared - using the LDAP StringPrep
 // profile of RFC 4518, with case folding and whitespace compression.
 // However, because it is optional for 2459/3280 implementations and because
 // it's desirable to avoid the size cost of the StringPrep tables,
 // this function treats |output| as if it was composed of ASCII.
 //
 // That is, rather than folding all whitespace characters, it only
 // folds ' '. Rather than case folding using locale-aware handling,
 // it only folds A-Z to a-z.
 //
 // This gives better results than outright rejecting (due to mismatched
 // encodings), or from doing a strict binary comparison (the minimum
 // required by RFC 3280), and is sufficient for those certificates
 // publicly deployed.
 //
 // If |charset_enforcement| is not NO_ENFORCEMENT and |output| contains any
 // characters not allowed in the specified charset, returns false.
 //
 // NOTE: |output| will be modified regardless of the return.
 [[nodiscard]] bool NormalizeDirectoryString(
     CharsetEnforcement charset_enforcement,
     std::string* output) {
   // Normalized version will always be equal or shorter than input.
   // Normalize in place and then truncate the output if necessary.
   std::string::const_iterator read_iter = output->begin();
   std::string::iterator write_iter = output->begin();

   for (; read_iter != output->end() && *read_iter == ' '; ++read_iter) {
     // Ignore leading whitespace.
   }

   for (; read_iter != output->end(); ++read_iter) {
     const unsigned char c = *read_iter;
     if (c == ' ') {
       // If there are non-whitespace characters remaining in input, compress
       // multiple whitespace chars to a single space, otherwise ignore trailing
       // whitespace.
       std::string::const_iterator next_iter = read_iter + 1;
       if (next_iter != output->end() && *next_iter != ' ')
         *(write_iter++) = ' ';
     } else if (c >= 'A' && c <= 'Z') {
       // Fold case.
       *(write_iter++) = c + ('a' - 'A');
     } else {
       // Note that these checks depend on the characters allowed by earlier
       // conditions also being valid for the enforced charset.
       switch (charset_enforcement) {
         case ENFORCE_PRINTABLE_STRING:
           // See NormalizePrintableStringValue comment for the acceptable list
           // of characters.
           if (!((c >= 'a' && c <= 'z') || (c >= '\'' && c <= ':') || c == '=' ||
                 c == '?'))
             return false;
           break;
         case ENFORCE_ASCII:
           if (c > 0x7F)
             return false;
           break;
         case NO_ENFORCEMENT:
           break;
       }
       *(write_iter++) = c;
     }
   }
   if (write_iter != output->end())
     output->erase(write_iter, output->end());
   return true;
 }

 // Converts the value of X509NameAttribute |attribute| to UTF-8, normalizes it,
 // and stores in |output|. The type of |attribute| must be one of the types for
 // which IsNormalizableDirectoryString is true.
 //
 // If the value of |attribute| can be normalized, returns true and sets
 // |output| to the case folded, normalized value. If the value of |attribute|
 // is invalid, returns false.
 // NOTE: |output| will be modified regardless of the return.
 [[nodiscard]] bool NormalizeValue(X509NameAttribute attribute,
                                   std::string* output,
                                   CertErrors* errors) {
   DCHECK(errors);

   if (!attribute.ValueAsStringUnsafe(output)) {
     errors->AddError(kFailedConvertingAttributeValue,
                      CreateCertErrorParams1SizeT("tag", attribute.value_tag));
     return false;
   }

   bool success = false;
   switch (attribute.value_tag) {
     case der::kPrintableString:
       success = NormalizeDirectoryString(ENFORCE_PRINTABLE_STRING, output);
       break;
     case der::kBmpString:
     case der::kUniversalString:
     case der::kUtf8String:
       success = NormalizeDirectoryString(NO_ENFORCEMENT, output);
       break;
     case der::kIA5String:
       success = NormalizeDirectoryString(ENFORCE_ASCII, output);
       break;
     default:
       // NOTREACHED
       success = false;
       break;
   }

   if (!success) {
     errors->AddError(kFailedNormalizingString,
                      CreateCertErrorParams1SizeT("tag", attribute.value_tag));
   }

   return success;
 }

 // Returns true if |tag| is a string type that NormalizeValue can handle.
 bool IsNormalizableDirectoryString(der::Tag tag) {
   switch (tag) {
     case der::kPrintableString:
     case der::kUtf8String:
     // RFC 5280 only requires handling IA5String for comparing domainComponent
     // values, but handling it here avoids the need to special case anything.
     case der::kIA5String:
     case der::kUniversalString:
     case der::kBmpString:
       return true;
     // TeletexString isn't normalized. Section 8 of RFC 5280 briefly
     // describes the historical confusion between treating TeletexString
     // as Latin1String vs T.61, and there are even incompatibilities within
     // T.61 implementations. As this time is virtually unused, simply
     // treat it with a binary comparison, as permitted by RFC 3280/5280.
     default:
       return false;
   }
 }

 // Returns true if the value of X509NameAttribute |a| matches |b|.
 bool VerifyValueMatch(X509NameAttribute a, X509NameAttribute b) {
   if (IsNormalizableDirectoryString(a.value_tag) &&
       IsNormalizableDirectoryString(b.value_tag)) {
     std::string a_normalized, b_normalized;
     // TODO(eroman): Plumb this down.
     CertErrors unused_errors;
     if (!NormalizeValue(a, &a_normalized, &unused_errors) ||
         !NormalizeValue(b, &b_normalized, &unused_errors))
       return false;
     return a_normalized == b_normalized;
   }
   // Attributes encoded with different types may be assumed to be unequal.
   if (a.value_tag != b.value_tag)
     return false;
   // All other types use binary comparison.
   return a.value == b.value;
 }

 // Verifies that |a_parser| and |b_parser| are the same length and that every
 // AttributeTypeAndValue in |a_parser| has a matching AttributeTypeAndValue in
 // |b_parser|.
 bool VerifyRdnMatch(der::Parser* a_parser, der::Parser* b_parser) {
   RelativeDistinguishedName a_type_and_values, b_type_and_values;
   if (!ReadRdn(a_parser, &a_type_and_values) ||
       !ReadRdn(b_parser, &b_type_and_values))
     return false;

   // RFC 5280 section 7.1:
   // Two relative distinguished names RDN1 and RDN2 match if they have the same
   // number of naming attributes and for each naming attribute in RDN1 there is
   // a matching naming attribute in RDN2.
   if (a_type_and_values.size() != b_type_and_values.size())
     return false;

   // The ordering of elements may differ due to denormalized values sorting
   // differently in the DER encoding. Since the number of elements should be
   // small, a naive linear search for each element should be fine. (Hostile
   // certificates already have ways to provoke pathological behavior.)
   for (const auto& a : a_type_and_values) {
     auto b_iter = b_type_and_values.begin();
     for (; b_iter != b_type_and_values.end(); ++b_iter) {
       const auto& b = *b_iter;
       if (a.type == b.type && VerifyValueMatch(a, b)) {
         break;
       }
     }
     if (b_iter == b_type_and_values.end())
       return false;
     // Remove the matched element from b_type_and_values to ensure duplicate
     // elements in a_type_and_values can't match the same element in
     // b_type_and_values multiple times.
     b_type_and_values.erase(b_iter);
   }

   // Every element in |a_type_and_values| had a matching element in
   // |b_type_and_values|.
   return true;
 }

 enum NameMatchType {
   EXACT_MATCH,
   SUBTREE_MATCH,
 };

 // Verify that |a| matches |b|. If |match_type| is EXACT_MATCH, returns true if
 // they are an exact match as defined by RFC 5280 7.1. If |match_type| is
 // SUBTREE_MATCH, returns true if |a| is within the subtree defined by |b| as
 // defined by RFC 5280 7.1.
 //
 // |a| and |b| are ASN.1 RDNSequence values (not including the Sequence tag),
 // defined in RFC 5280 section 4.1.2.4:
 //
 // Name ::= CHOICE { -- only one possibility for now --
 //   rdnSequence  RDNSequence }
 //
 // RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
 //
 // RelativeDistinguishedName ::=
 //   SET SIZE (1..MAX) OF AttributeTypeAndValue
 bool VerifyNameMatchInternal(const der::Input& a,
                              const der::Input& b,
                              NameMatchType match_type) {
   // Empty Names are allowed.  RFC 5280 section 4.1.2.4 requires "The issuer
   // field MUST contain a non-empty distinguished name (DN)", while section
   // 4.1.2.6 allows for the Subject to be empty in certain cases. The caller is
   // assumed to have verified those conditions.

   // RFC 5280 section 7.1:
   // Two distinguished names DN1 and DN2 match if they have the same number of
   // RDNs, for each RDN in DN1 there is a matching RDN in DN2, and the matching
   // RDNs appear in the same order in both DNs.

   // As an optimization, first just compare the number of RDNs:
   der::Parser a_rdn_sequence_counter(a);
   der::Parser b_rdn_sequence_counter(b);
   while (a_rdn_sequence_counter.HasMore() && b_rdn_sequence_counter.HasMore()) {
     if (!a_rdn_sequence_counter.SkipTag(der::kSet) ||
         !b_rdn_sequence_counter.SkipTag(der::kSet)) {
       return false;
     }
   }
   // If doing exact match and either of the sequences has more elements than the
   // other, not a match. If doing a subtree match, the first Name may have more
   // RDNs than the second.
   if (b_rdn_sequence_counter.HasMore())
     return false;
   if (match_type == EXACT_MATCH && a_rdn_sequence_counter.HasMore())
     return false;

   // Verify that RDNs in |a| and |b| match.
   der::Parser a_rdn_sequence(a);
   der::Parser b_rdn_sequence(b);
   while (a_rdn_sequence.HasMore() && b_rdn_sequence.HasMore()) {
     der::Parser a_rdn, b_rdn;
     if (!a_rdn_sequence.ReadConstructed(der::kSet, &a_rdn) ||
         !b_rdn_sequence.ReadConstructed(der::kSet, &b_rdn)) {
       return false;
     }
     if (!VerifyRdnMatch(&a_rdn, &b_rdn))
       return false;
   }

   return true;
 }

 }  // namespace

 bool NormalizeName(const der::Input& name_rdn_sequence,
                    std::string* normalized_rdn_sequence,
                    CertErrors* errors) {
   DCHECK(errors);

   // RFC 5280 section 4.1.2.4
   // RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
   der::Parser rdn_sequence_parser(name_rdn_sequence);

   bssl::ScopedCBB cbb;
   if (!CBB_init(cbb.get(), 0))
     return false;

   while (rdn_sequence_parser.HasMore()) {
     // RelativeDistinguishedName ::= SET SIZE (1..MAX) OF AttributeTypeAndValue
     der::Parser rdn_parser;
     if (!rdn_sequence_parser.ReadConstructed(der::kSet, &rdn_parser))
       return false;
     RelativeDistinguishedName type_and_values;
     if (!ReadRdn(&rdn_parser, &type_and_values))
       return false;

     CBB rdn_cbb;
     if (!CBB_add_asn1(cbb.get(), &rdn_cbb, CBS_ASN1_SET))
       return false;

     for (const auto& type_and_value : type_and_values) {
       // AttributeTypeAndValue ::= SEQUENCE {
       //   type     AttributeType,
       //   value    AttributeValue }
       CBB attribute_type_and_value_cbb, type_cbb, value_cbb;
       if (!CBB_add_asn1(&rdn_cbb, &attribute_type_and_value_cbb,
                         CBS_ASN1_SEQUENCE)) {
         return false;
       }

       // AttributeType ::= OBJECT IDENTIFIER
       if (!CBB_add_asn1(&attribute_type_and_value_cbb, &type_cbb,
                         CBS_ASN1_OBJECT) ||
           !CBB_add_bytes(&type_cbb, type_and_value.type.UnsafeData(),
                          type_and_value.type.Length())) {
         return false;
       }

       // AttributeValue ::= ANY -- DEFINED BY AttributeType
       if (IsNormalizableDirectoryString(type_and_value.value_tag)) {
         std::string normalized_value;
         if (!NormalizeValue(type_and_value, &normalized_value, errors))
           return false;
         if (!CBB_add_asn1(&attribute_type_and_value_cbb, &value_cbb,
                           CBS_ASN1_UTF8STRING) ||
             !CBB_add_bytes(
                 &value_cbb,
                 reinterpret_cast<const uint8_t*>(normalized_value.data()),
                 normalized_value.size()))
           return false;
       } else {
         if (!CBB_add_asn1(&attribute_type_and_value_cbb, &value_cbb,
                           type_and_value.value_tag) ||
             !CBB_add_bytes(&value_cbb, type_and_value.value.UnsafeData(),
                            type_and_value.value.Length()))
           return false;
       }

       if (!CBB_flush(&rdn_cbb))
         return false;
     }

     // Ensure the encoded AttributeTypeAndValue values in the SET OF are sorted.
     if (!CBB_flush_asn1_set_of(&rdn_cbb) || !CBB_flush(cbb.get()))
       return false;
   }

   normalized_rdn_sequence->assign(CBB_data(cbb.get()),
                                   CBB_data(cbb.get()) + CBB_len(cbb.get()));
   return true;
 }

 bool VerifyNameMatch(const der::Input& a_rdn_sequence,
                      const der::Input& b_rdn_sequence) {
   return VerifyNameMatchInternal(a_rdn_sequence, b_rdn_sequence, EXACT_MATCH);
 }

 bool VerifyNameInSubtree(const der::Input& name_rdn_sequence,
                          const der::Input& parent_rdn_sequence) {
   return VerifyNameMatchInternal(name_rdn_sequence, parent_rdn_sequence,
                                  SUBTREE_MATCH);
 }

 bool FindEmailAddressesInName(
     const der::Input& name_rdn_sequence,
     std::vector<std::string>* contained_email_addresses) {
   contained_email_addresses->clear();

   der::Parser rdn_sequence_parser(name_rdn_sequence);
   while (rdn_sequence_parser.HasMore()) {
     der::Parser rdn_parser;
     if (!rdn_sequence_parser.ReadConstructed(der::kSet, &rdn_parser))
       return false;

     RelativeDistinguishedName type_and_values;
     if (!ReadRdn(&rdn_parser, &type_and_values))
       return false;

     for (const auto& type_and_value : type_and_values) {
       if (type_and_value.type == der::Input(kTypeEmailAddressOid)) {
         std::string email_address;
         if (!type_and_value.ValueAsString(&email_address)) {
           return false;
         }
         contained_email_addresses->push_back(std::move(email_address));
       }
     }
   }

   return true;
 }

 }  // namespace net
	// Copyright 2015 The Chromium Authors
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#include "verify_name_match.h"

	#include "cert_error_params.h"
	#include "cert_errors.h"
	#include "parse_name.h"
	#include "input.h"
	#include "parser.h"
	#include "tag.h"
	#include <openssl/bytestring.h>

	namespace bssl {

	DEFINE_CERT_ERROR_ID(kFailedConvertingAttributeValue,
	"Failed converting AttributeValue to string");
	DEFINE_CERT_ERROR_ID(kFailedNormalizingString, "Failed normalizing string");

	namespace {

	// Types of character set checking that NormalizeDirectoryString can perform.
	enum CharsetEnforcement {
	NO_ENFORCEMENT,
	ENFORCE_PRINTABLE_STRING,
	ENFORCE_ASCII,
	};

	// Normalizes \|output\|, a UTF-8 encoded string, as if it contained
	// only ASCII characters.
	//
	// This could be considered a partial subset of RFC 5280 rules, and
	// is compatible with RFC 2459/3280.
	//
	// In particular, RFC 5280, Section 7.1 describes how UTF8String
	// and PrintableString should be compared - using the LDAP StringPrep
	// profile of RFC 4518, with case folding and whitespace compression.
	// However, because it is optional for 2459/3280 implementations and because
	// it's desirable to avoid the size cost of the StringPrep tables,
	// this function treats \|output\| as if it was composed of ASCII.
	//
	// That is, rather than folding all whitespace characters, it only
	// folds ' '. Rather than case folding using locale-aware handling,
	// it only folds A-Z to a-z.
	//
	// This gives better results than outright rejecting (due to mismatched
	// encodings), or from doing a strict binary comparison (the minimum
	// required by RFC 3280), and is sufficient for those certificates
	// publicly deployed.
	//
	// If \|charset_enforcement\| is not NO_ENFORCEMENT and \|output\| contains any
	// characters not allowed in the specified charset, returns false.
	//
	// NOTE: \|output\| will be modified regardless of the return.
	[[nodiscard]] bool NormalizeDirectoryString(
	CharsetEnforcement charset_enforcement,
	std::string* output) {
	// Normalized version will always be equal or shorter than input.
	// Normalize in place and then truncate the output if necessary.
	std::string::const_iterator read_iter = output->begin();
	std::string::iterator write_iter = output->begin();

	for (; read_iter != output->end() && *read_iter == ' '; ++read_iter) {
	// Ignore leading whitespace.
	}

	for (; read_iter != output->end(); ++read_iter) {
	const unsigned char c = *read_iter;
	if (c == ' ') {
	// If there are non-whitespace characters remaining in input, compress
	// multiple whitespace chars to a single space, otherwise ignore trailing
	// whitespace.
	std::string::const_iterator next_iter = read_iter + 1;
	if (next_iter != output->end() && *next_iter != ' ')
	*(write_iter++) = ' ';
	} else if (c >= 'A' && c <= 'Z') {
	// Fold case.
	*(write_iter++) = c + ('a' - 'A');
	} else {
	// Note that these checks depend on the characters allowed by earlier
	// conditions also being valid for the enforced charset.
	switch (charset_enforcement) {
	case ENFORCE_PRINTABLE_STRING:
	// See NormalizePrintableStringValue comment for the acceptable list
	// of characters.
	if (!((c >= 'a' && c <= 'z') \|\| (c >= '\'' && c <= ':') \|\| c == '=' \|\|
	c == '?'))
	return false;
	break;
	case ENFORCE_ASCII:
	if (c > 0x7F)
	return false;
	break;
	case NO_ENFORCEMENT:
	break;
	}
	*(write_iter++) = c;
	}
	}
	if (write_iter != output->end())
	output->erase(write_iter, output->end());
	return true;
	}

	// Converts the value of X509NameAttribute \|attribute\| to UTF-8, normalizes it,
	// and stores in \|output\|. The type of \|attribute\| must be one of the types for
	// which IsNormalizableDirectoryString is true.
	//
	// If the value of \|attribute\| can be normalized, returns true and sets
	// \|output\| to the case folded, normalized value. If the value of \|attribute\|
	// is invalid, returns false.
	// NOTE: \|output\| will be modified regardless of the return.
	[[nodiscard]] bool NormalizeValue(X509NameAttribute attribute,
	std::string* output,
	CertErrors* errors) {
	DCHECK(errors);

	if (!attribute.ValueAsStringUnsafe(output)) {
	errors->AddError(kFailedConvertingAttributeValue,
	CreateCertErrorParams1SizeT("tag", attribute.value_tag));
	return false;
	}

	bool success = false;
	switch (attribute.value_tag) {
	case der::kPrintableString:
	success = NormalizeDirectoryString(ENFORCE_PRINTABLE_STRING, output);
	break;
	case der::kBmpString:
	case der::kUniversalString:
	case der::kUtf8String:
	success = NormalizeDirectoryString(NO_ENFORCEMENT, output);
	break;
	case der::kIA5String:
	success = NormalizeDirectoryString(ENFORCE_ASCII, output);
	break;
	default:
	// NOTREACHED
	success = false;
	break;
	}

	if (!success) {
	errors->AddError(kFailedNormalizingString,
	CreateCertErrorParams1SizeT("tag", attribute.value_tag));
	}

	return success;
	}

	// Returns true if \|tag\| is a string type that NormalizeValue can handle.
	bool IsNormalizableDirectoryString(der::Tag tag) {
	switch (tag) {
	case der::kPrintableString:
	case der::kUtf8String:
	// RFC 5280 only requires handling IA5String for comparing domainComponent
	// values, but handling it here avoids the need to special case anything.
	case der::kIA5String:
	case der::kUniversalString:
	case der::kBmpString:
	return true;
	// TeletexString isn't normalized. Section 8 of RFC 5280 briefly
	// describes the historical confusion between treating TeletexString
	// as Latin1String vs T.61, and there are even incompatibilities within
	// T.61 implementations. As this time is virtually unused, simply
	// treat it with a binary comparison, as permitted by RFC 3280/5280.
	default:
	return false;
	}
	}

	// Returns true if the value of X509NameAttribute \|a\| matches \|b\|.
	bool VerifyValueMatch(X509NameAttribute a, X509NameAttribute b) {
	if (IsNormalizableDirectoryString(a.value_tag) &&
	IsNormalizableDirectoryString(b.value_tag)) {
	std::string a_normalized, b_normalized;
	// TODO(eroman): Plumb this down.
	CertErrors unused_errors;
	if (!NormalizeValue(a, &a_normalized, &unused_errors) \|\|
	!NormalizeValue(b, &b_normalized, &unused_errors))
	return false;
	return a_normalized == b_normalized;
	}
	// Attributes encoded with different types may be assumed to be unequal.
	if (a.value_tag != b.value_tag)
	return false;
	// All other types use binary comparison.
	return a.value == b.value;
	}

	// Verifies that \|a_parser\| and \|b_parser\| are the same length and that every
	// AttributeTypeAndValue in \|a_parser\| has a matching AttributeTypeAndValue in
	// \|b_parser\|.
	bool VerifyRdnMatch(der::Parser* a_parser, der::Parser* b_parser) {
	RelativeDistinguishedName a_type_and_values, b_type_and_values;
	if (!ReadRdn(a_parser, &a_type_and_values) \|\|
	!ReadRdn(b_parser, &b_type_and_values))
	return false;

	// RFC 5280 section 7.1:
	// Two relative distinguished names RDN1 and RDN2 match if they have the same
	// number of naming attributes and for each naming attribute in RDN1 there is
	// a matching naming attribute in RDN2.
	if (a_type_and_values.size() != b_type_and_values.size())
	return false;

	// The ordering of elements may differ due to denormalized values sorting
	// differently in the DER encoding. Since the number of elements should be
	// small, a naive linear search for each element should be fine. (Hostile
	// certificates already have ways to provoke pathological behavior.)
	for (const auto& a : a_type_and_values) {
	auto b_iter = b_type_and_values.begin();
	for (; b_iter != b_type_and_values.end(); ++b_iter) {
	const auto& b = *b_iter;
	if (a.type == b.type && VerifyValueMatch(a, b)) {
	break;
	}
	}
	if (b_iter == b_type_and_values.end())
	return false;
	// Remove the matched element from b_type_and_values to ensure duplicate
	// elements in a_type_and_values can't match the same element in
	// b_type_and_values multiple times.
	b_type_and_values.erase(b_iter);
	}

	// Every element in \|a_type_and_values\| had a matching element in
	// \|b_type_and_values\|.
	return true;
	}

	enum NameMatchType {
	EXACT_MATCH,
	SUBTREE_MATCH,
	};

	// Verify that \|a\| matches \|b\|. If \|match_type\| is EXACT_MATCH, returns true if
	// they are an exact match as defined by RFC 5280 7.1. If \|match_type\| is
	// SUBTREE_MATCH, returns true if \|a\| is within the subtree defined by \|b\| as
	// defined by RFC 5280 7.1.
	//
	// \|a\| and \|b\| are ASN.1 RDNSequence values (not including the Sequence tag),
	// defined in RFC 5280 section 4.1.2.4:
	//
	// Name ::= CHOICE { -- only one possibility for now --
	// rdnSequence RDNSequence }
	//
	// RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
	//
	// RelativeDistinguishedName ::=
	// SET SIZE (1..MAX) OF AttributeTypeAndValue
	bool VerifyNameMatchInternal(const der::Input& a,
	const der::Input& b,
	NameMatchType match_type) {
	// Empty Names are allowed. RFC 5280 section 4.1.2.4 requires "The issuer
	// field MUST contain a non-empty distinguished name (DN)", while section
	// 4.1.2.6 allows for the Subject to be empty in certain cases. The caller is
	// assumed to have verified those conditions.

	// RFC 5280 section 7.1:
	// Two distinguished names DN1 and DN2 match if they have the same number of
	// RDNs, for each RDN in DN1 there is a matching RDN in DN2, and the matching
	// RDNs appear in the same order in both DNs.

	// As an optimization, first just compare the number of RDNs:
	der::Parser a_rdn_sequence_counter(a);
	der::Parser b_rdn_sequence_counter(b);
	while (a_rdn_sequence_counter.HasMore() && b_rdn_sequence_counter.HasMore()) {
	if (!a_rdn_sequence_counter.SkipTag(der::kSet) \|\|
	!b_rdn_sequence_counter.SkipTag(der::kSet)) {
	return false;
	}
	}
	// If doing exact match and either of the sequences has more elements than the
	// other, not a match. If doing a subtree match, the first Name may have more
	// RDNs than the second.
	if (b_rdn_sequence_counter.HasMore())
	return false;
	if (match_type == EXACT_MATCH && a_rdn_sequence_counter.HasMore())
	return false;

	// Verify that RDNs in \|a\| and \|b\| match.
	der::Parser a_rdn_sequence(a);
	der::Parser b_rdn_sequence(b);
	while (a_rdn_sequence.HasMore() && b_rdn_sequence.HasMore()) {
	der::Parser a_rdn, b_rdn;
	if (!a_rdn_sequence.ReadConstructed(der::kSet, &a_rdn) \|\|
	!b_rdn_sequence.ReadConstructed(der::kSet, &b_rdn)) {
	return false;
	}
	if (!VerifyRdnMatch(&a_rdn, &b_rdn))
	return false;
	}

	return true;
	}

	} // namespace

	bool NormalizeName(const der::Input& name_rdn_sequence,
	std::string* normalized_rdn_sequence,
	CertErrors* errors) {
	DCHECK(errors);

	// RFC 5280 section 4.1.2.4
	// RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
	der::Parser rdn_sequence_parser(name_rdn_sequence);

	bssl::ScopedCBB cbb;
	if (!CBB_init(cbb.get(), 0))
	return false;

	while (rdn_sequence_parser.HasMore()) {
	// RelativeDistinguishedName ::= SET SIZE (1..MAX) OF AttributeTypeAndValue
	der::Parser rdn_parser;
	if (!rdn_sequence_parser.ReadConstructed(der::kSet, &rdn_parser))
	return false;
	RelativeDistinguishedName type_and_values;
	if (!ReadRdn(&rdn_parser, &type_and_values))
	return false;

	CBB rdn_cbb;
	if (!CBB_add_asn1(cbb.get(), &rdn_cbb, CBS_ASN1_SET))
	return false;

	for (const auto& type_and_value : type_and_values) {
	// AttributeTypeAndValue ::= SEQUENCE {
	// type AttributeType,
	// value AttributeValue }
	CBB attribute_type_and_value_cbb, type_cbb, value_cbb;
	if (!CBB_add_asn1(&rdn_cbb, &attribute_type_and_value_cbb,
	CBS_ASN1_SEQUENCE)) {
	return false;
	}

	// AttributeType ::= OBJECT IDENTIFIER
	if (!CBB_add_asn1(&attribute_type_and_value_cbb, &type_cbb,
	CBS_ASN1_OBJECT) \|\|
	!CBB_add_bytes(&type_cbb, type_and_value.type.UnsafeData(),
	type_and_value.type.Length())) {
	return false;
	}

	// AttributeValue ::= ANY -- DEFINED BY AttributeType
	if (IsNormalizableDirectoryString(type_and_value.value_tag)) {
	std::string normalized_value;
	if (!NormalizeValue(type_and_value, &normalized_value, errors))
	return false;
	if (!CBB_add_asn1(&attribute_type_and_value_cbb, &value_cbb,
	CBS_ASN1_UTF8STRING) \|\|
	!CBB_add_bytes(
	&value_cbb,
	reinterpret_cast<const uint8_t*>(normalized_value.data()),
	normalized_value.size()))
	return false;
	} else {
	if (!CBB_add_asn1(&attribute_type_and_value_cbb, &value_cbb,
	type_and_value.value_tag) \|\|
	!CBB_add_bytes(&value_cbb, type_and_value.value.UnsafeData(),
	type_and_value.value.Length()))
	return false;
	}

	if (!CBB_flush(&rdn_cbb))
	return false;
	}

	// Ensure the encoded AttributeTypeAndValue values in the SET OF are sorted.
	if (!CBB_flush_asn1_set_of(&rdn_cbb) \|\| !CBB_flush(cbb.get()))
	return false;
	}

	normalized_rdn_sequence->assign(CBB_data(cbb.get()),
	CBB_data(cbb.get()) + CBB_len(cbb.get()));
	return true;
	}

	bool VerifyNameMatch(const der::Input& a_rdn_sequence,
	const der::Input& b_rdn_sequence) {
	return VerifyNameMatchInternal(a_rdn_sequence, b_rdn_sequence, EXACT_MATCH);
	}

	bool VerifyNameInSubtree(const der::Input& name_rdn_sequence,
	const der::Input& parent_rdn_sequence) {
	return VerifyNameMatchInternal(name_rdn_sequence, parent_rdn_sequence,
	SUBTREE_MATCH);
	}

	bool FindEmailAddressesInName(
	const der::Input& name_rdn_sequence,
	std::vector<std::string>* contained_email_addresses) {
	contained_email_addresses->clear();

	der::Parser rdn_sequence_parser(name_rdn_sequence);
	while (rdn_sequence_parser.HasMore()) {
	der::Parser rdn_parser;
	if (!rdn_sequence_parser.ReadConstructed(der::kSet, &rdn_parser))
	return false;

	RelativeDistinguishedName type_and_values;
	if (!ReadRdn(&rdn_parser, &type_and_values))
	return false;

	for (const auto& type_and_value : type_and_values) {
	if (type_and_value.type == der::Input(kTypeEmailAddressOid)) {
	std::string email_address;
	if (!type_and_value.ValueAsString(&email_address)) {
	return false;
	}
	contained_email_addresses->push_back(std::move(email_address));
	}
	}
	}

	return true;
	}

	} // namespace net