Add DER parsing for rsaPss signature algorithms.

net/cert/internal/signature_algorithm.cc

Index: net/cert/internal/signature_algorithm.cc
diff --git a/net/cert/internal/signature_algorithm.cc b/net/cert/internal/signature_algorithm.cc
index 2a4ce7678fbf0bc4ff664d9fd93de8f589c64585..7be9073ea74283d28f9c97815b130c28a52b4e96 100644
--- a/net/cert/internal/signature_algorithm.cc
+++ b/net/cert/internal/signature_algorithm.cc
@@ -6,7 +6,9 @@
 
 #include <stdint.h>
 
+#include "base/numerics/safe_math.h"
 #include "net/der/input.h"
+#include "net/der/parse_values.h"
 #include "net/der/parser.h"
 
 namespace net {
@@ -96,6 +98,43 @@ const uint8_t kOidEcdsaWithSha512[] =
 const uint8_t kOidRsaSsaPss[] =
     {0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x01, 0x0a};
 
+// From RFC 4055:
+//   id-sha1  OBJECT IDENTIFIER  ::=  { iso(1)
+//                        identified-organization(3) oiw(14)
+//                        secsig(3) algorithms(2) 26 }
+// In dotted notation: 1.3.14.3.2.26
+const uint8_t kOidSha1[] = {0x2B, 0x0E, 0x03, 0x02, 0x1A};
+
+// From RFC 4055:
+//   id-sha256  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
+//                        country(16) us(840) organization(1) gov(101)
+//                        csor(3) nistalgorithm(4) hashalgs(2) 1 }
+// In dotted notation: 2.16.840.1.101.3.4.2.1
+const uint8_t kOidSha256[] =
+    {0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01};
+
+// From RFC 4055:
+//   id-sha384  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
+//                        country(16) us(840) organization(1) gov(101)
+//                        csor(3) nistalgorithm(4) hashalgs(2) 2 }
+// In dotted notation: 2.16.840.1.101.3.4.2.2
+const uint8_t kOidSha384[] =
+    {0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02};
+
+// From RFC 4055:
+//   id-sha512  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
+//                        country(16) us(840) organization(1) gov(101)
+//                        csor(3) nistalgorithm(4) hashalgs(2) 3 }
+// In dotted notation: 2.16.840.1.101.3.4.2.3
+const uint8_t kOidSha512[] =
+    {0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03};
+
+// From RFC 4055:
+//   id-mgf1  OBJECT IDENTIFIER  ::=  { pkcs-1 8 }
+// In dotted notation: 1.2.840.113549.1.1.8
+const uint8_t kOidMgf1[] =
+    {0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x01, 0x08};
+
 // RFC 5280 section 4.1.1.2 defines signatureAlgorithm as:
 //
 //  AlgorithmIdentifier  ::=  SEQUENCE  {
@@ -207,6 +246,126 @@ WARN_UNUSED_RESULT bool ParseEcdsa(DigestAlgorithm digest,
   return true;
 }
 
+// Parses an AlgorithmIdentifier representing an RFC 4055 "HashAlgorithm".
+// Examples of HashAlgorithms are:
+//
+//      sha1Identifier  AlgorithmIdentifier  ::=  { id-sha1, NULL }
+//      sha224Identifier  AlgorithmIdentifier  ::=  { id-sha224, NULL }
+//      sha256Identifier  AlgorithmIdentifier  ::=  { id-sha256, NULL }
+//      sha384Identifier  AlgorithmIdentifier  ::=  { id-sha384, NULL }
+//      sha512Identifier  AlgorithmIdentifier  ::=  { id-sha512, NULL }
+//
+// Note that the parameters needn't be NULL as in the examples above. RFC 4055
+// says that:
+//
+//    All implementations MUST accept both NULL and absent parameters as
+//    legal and equivalent encodings.
+WARN_UNUSED_RESULT bool ParseHashAlgorithm(const der::Input input,
+                                           DigestAlgorithm* out) {
+  der::Input oid;
+  der::Input params;
+  if (!ParseAlgorithmIdentifier(input, &oid, &params))
+    return false;
+
+  DigestAlgorithm hash;
+
+  if (oid.Equals(der::Input(kOidSha1))) {
+    hash = DigestAlgorithm::Sha1;
+  } else if (oid.Equals(der::Input(kOidSha256))) {
+    hash = DigestAlgorithm::Sha256;
+  } else if (oid.Equals(der::Input(kOidSha384))) {
+    hash = DigestAlgorithm::Sha384;
+  } else if (oid.Equals(der::Input(kOidSha512))) {
+    hash = DigestAlgorithm::Sha512;
+  } else {
+    // Unsupported digest algorithm.
+    return false;
+  }
+
+  if (!IsNullOrEmpty(params))
+    return false;
+
+  *out = hash;
+  return true;
+}
+
+// Parses a MaskGenAlgorithm as defined by RFC 4055:
+//
+//     MaskGenAlgorithm  ::=  AlgorithmIdentifier
+//
+// This function currently only supports MGF1, as that is the only function
+// defined in RFC 4055.
+//
+// RFC 4055 section 2.2:
+//
+//     One mask generation function is used with the RSASSA-PSS signature
+//     algorithm and the RSAES-OAEP key transport algorithm: MGF1 [P1v2.1].
+//     No other mask generation functions are supported by this
+//     specification.
+//
+//     MGF1 is identified by the following object identifier:
+//
+//        id-mgf1  OBJECT IDENTIFIER  ::=  { pkcs-1 8 }
+//
+//     The parameters field associated with id-mgf1 MUST have a
+//     hashAlgorithm value which identifies the hash function being used
+//     with MGF1.  This value MUST be sha1Identifier, sha224Identifier,
+//     sha256Identifier, sha384Identifier, or sha512Identifier, as specified
+//     in Section 2.1.  Implementations MUST support the default value,
+//     sha1Identifier, and MAY support the other four values.
+WARN_UNUSED_RESULT bool ParseMaskGenAlgorithm(const der::Input input,
+                                              DigestAlgorithm* mgf1_hash) {
+  der::Input oid;
+  der::Input params;
+  if (!ParseAlgorithmIdentifier(input, &oid, &params))
+    return false;
+
+  // MGF1 is the only supported mask generation algorithm.
+  if (!oid.Equals(der::Input(kOidMgf1)))
+    return false;
+
+  return ParseHashAlgorithm(params, mgf1_hash);
+}
+
+// Consumes an optional, explicitly-tagged INTEGER from |parser|, using the
+// indicated context-specific class number. Values greater than 32-bits will be
+// rejected.
+//
+// Returns true on success and sets |*present| to true if the field was present.
+WARN_UNUSED_RESULT bool ReadOptionalContextSpecificUint32(der::Parser* parser,
+                                                          uint8_t class_number,
+                                                          uint32_t* out,
+                                                          bool* present) {
+  der::Input value;
+  bool has_value;
+
+  // Read the context specific value.
+  if (!parser->ReadOptionalTag(der::ContextSpecificConstructed(class_number),
+                               &value, &has_value)) {
+    return false;
+  }
+
+  if (has_value) {
+    // Parse the integer contained in it.
+    der::Parser number_parser(value);
+    uint64_t uint64_value;
+
+    if (!number_parser.ReadUint64(&uint64_value))
+      return false;
+    if (number_parser.HasMore())
+      return false;
+
+    // Cast the number to a uint32_t
+    base::CheckedNumeric<uint32_t> casted(uint64_value);
+    if (!casted.IsValid())
+      return false;
+    *out = casted.ValueOrDie();
+  }
+
+  *present = has_value;
+  return true;
+}
+
 // From RFC 4055:
 //    RSASSA-PSS-params  ::=  SEQUENCE  {
 //         hashAlgorithm     [0] HashAlgorithm DEFAULT
@@ -221,8 +380,73 @@ WARN_UNUSED_RESULT bool ParseEcdsa(DigestAlgorithm digest,
 //      MaskGenAlgorithm  ::=  AlgorithmIdentifier
 WARN_UNUSED_RESULT bool ParseRsaPss(const der::Input& params,
                                     SignatureAlgorithm* out) {
-  // TODO(eroman): Implement.
-  return false;
+  // RFC 4055 says that the RSASSA-PSS-params must be present in signature
+  // algorithms. (However because each field is optional, the sequence could be
+  // empty when using all the defaults).
+  //
+  // Section 3.1:
+  //
+  //    When RSASSA-PSS is used in an AlgorithmIdentifier, the parameters
+  //    MUST employ the RSASSA-PSS-params syntax.  The parameters may be
+  //    either absent or present when used as subject public key information.
+  //    The parameters MUST be present when used in the algorithm identifier
+  //    associated with a signature value.
+  der::Parser parser(params);
+  der::Parser params_parser;
+  if (!parser.ReadSequence(&params_parser))
+    return false;
+
+  // There shouldn't be anything after the sequence.
+  if (parser.HasMore())

[Ryan Sleevi, 2015/07/08 11:30:39]

This is fine

+    return false;
+
+  // Initialize parameters to their default values.
+  DigestAlgorithm hash = DigestAlgorithm::Sha1;
+  DigestAlgorithm mgf1_hash = DigestAlgorithm::Sha1;
+  uint32_t salt_length = 20u;
+  uint32_t trailer_field = 1u;
+
+  bool has_field;
+  der::Input field;
+
+  // Parse hashAlgorithm [0]
+  if (!params_parser.ReadOptionalTag(der::ContextSpecificConstructed(0), &field,
+                                     &has_field)) {
+    return false;
+  }
+  if (has_field && !ParseHashAlgorithm(field, &hash))
+    return false;
+
+  // Parse maskGenAlgorithm [1]
+  if (!params_parser.ReadOptionalTag(der::ContextSpecificConstructed(1), &field,
+                                     &has_field)) {
+    return false;
+  }
+  if (has_field && !ParseMaskGenAlgorithm(field, &mgf1_hash))
+    return false;
+
+  // Parse saltLength [2]
+  if (!ReadOptionalContextSpecificUint32(&params_parser, 2, &salt_length,
+                                         &has_field)) {
+    return false;
+  }
+
+  // Parse trailerField [3]
+  if (!ReadOptionalContextSpecificUint32(&params_parser, 3, &trailer_field,
+                                         &has_field)) {
+    return false;
+  }
+
+  // The trailer field MUST be 1 per RFC 4055.
+  if (trailer_field != 1)
+    return false;
+
+  // There must not be any unconsumed data left.
+  if (params_parser.HasMore())

[Ryan Sleevi, 2015/07/08 11:30:39]

The related discussion (re; RFC 5912, RFC 6025, re: X.680) concluded that this
is fine for this specific case, in that it's not explicitly defined as
extensible under the 2008 syntax (even though it is totally valid for a future
specification update to extend this, per X.680 and the 1998 syntax that it was
originally written under)

[eroman, 2015/07/14 20:50:27]

I have updated comments to reference RFC 5912, and provide justification for the
various HasMore() checks. 

+    return false;
+
+  out->AssignRsaPss(hash, mgf1_hash, salt_length);
+  return true;
 }
 
 }  // namespace