Add public key and signature verification to browser-side API keys

content/browser/experiments/api_key.cc

Index: content/browser/experiments/api_key.cc
diff --git a/content/browser/experiments/api_key.cc b/content/browser/experiments/api_key.cc
index 5ab842b68e0325e7bb40cac9adb2418f75e1d0fc..f7dfc53e7d59b3bb447531e7a45be1d4c54bcc2b 100644
--- a/content/browser/experiments/api_key.cc
+++ b/content/browser/experiments/api_key.cc
@@ -12,6 +12,31 @@
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/time/time.h"
+#include "crypto/signature_verifier.h"
+#include "net/cert/pem_tokenizer.h"
+
+namespace {
+
+// This is the default public key used for validating signatures.
+// TODO(iclelland): Move this to the embedder, and provide a mechanism to allow
+// for multiple signing keys. https://crbug.com/543220
+const char kPublicKeyPEM[] =
+    "-----BEGIN PUBLIC KEY-----"
+    "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA38CwBHcz8YoCnPVwhH1p"
+    "jzmz/TKFu1ggI0+gzugBE+esApjm4I9N1PJ3/GLa+qpzp/VpgyzWqXiRoGM/RCZA"
+    "V5U+kDaoukxA33GdeA3BUrcYBIaspGRx6xXX36HLLPJF6YdjxbEByYprzecXhNUI"
+    "ql5VW3D0IR4frU5FzPy/XB5iblFxZAG4682IRRL5KdGL4OWFAPuzaKOMq7ojeKA9"
+    "y8Gu29huRknKALuScxqk+Jn5Qf3zWckLTpwyPoooXDQ116vs0b9ssalRSuBSRh4Q"
+    "tjzoQ6S1S5Zqw+2rvXfYhVZ65iiR1zzz6nBXIuUm9HAzIIF43LE6akG9E/F93ZYN"
+    "mwIDAQAB"
+    "-----END PUBLIC KEY-----";

[davidben, 2015/12/18 22:23:17]

Here, use this:

static const uint8_t kPublicKey[] = {
    0x30, 0x82, 0x01, 0x22, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48, 0x86,
    0xf7, 0x0d, 0x01, 0x01, 0x01, 0x05, 0x00, 0x03, 0x82, 0x01, 0x0f, 0x00,
    0x30, 0x82, 0x01, 0x0a, 0x02, 0x82, 0x01, 0x01, 0x00, 0xdf, 0xc0, 0xb0,
    0x04, 0x77, 0x33, 0xf1, 0x8a, 0x02, 0x9c, 0xf5, 0x70, 0x84, 0x7d, 0x69,
    0x8f, 0x39, 0xb3, 0xfd, 0x32, 0x85, 0xbb, 0x58, 0x20, 0x23, 0x4f, 0xa0,
    0xce, 0xe8, 0x01, 0x13, 0xe7, 0xac, 0x02, 0x98, 0xe6, 0xe0, 0x8f, 0x4d,
    0xd4, 0xf2, 0x77, 0xfc, 0x62, 0xda, 0xfa, 0xaa, 0x73, 0xa7, 0xf5, 0x69,
    0x83, 0x2c, 0xd6, 0xa9, 0x78, 0x91, 0xa0, 0x63, 0x3f, 0x44, 0x26, 0x40,
    0x57, 0x95, 0x3e, 0x90, 0x36, 0xa8, 0xba, 0x4c, 0x40, 0xdf, 0x71, 0x9d,
    0x78, 0x0d, 0xc1, 0x52, 0xb7, 0x18, 0x04, 0x86, 0xac, 0xa4, 0x64, 0x71,
    0xeb, 0x15, 0xd7, 0xdf, 0xa1, 0xcb, 0x2c, 0xf2, 0x45, 0xe9, 0x87, 0x63,
    0xc5, 0xb1, 0x01, 0xc9, 0x8a, 0x6b, 0xcd, 0xe7, 0x17, 0x84, 0xd5, 0x08,
    0xaa, 0x5e, 0x55, 0x5b, 0x70, 0xf4, 0x21, 0x1e, 0x1f, 0xad, 0x4e, 0x45,
    0xcc, 0xfc, 0xbf, 0x5c, 0x1e, 0x62, 0x6e, 0x51, 0x71, 0x64, 0x01, 0xb8,
    0xeb, 0xcd, 0x88, 0x45, 0x12, 0xf9, 0x29, 0xd1, 0x8b, 0xe0, 0xe5, 0x85,
    0x00, 0xfb, 0xb3, 0x68, 0xa3, 0x8c, 0xab, 0xba, 0x23, 0x78, 0xa0, 0x3d,
    0xcb, 0xc1, 0xae, 0xdb, 0xd8, 0x6e, 0x46, 0x49, 0xca, 0x00, 0xbb, 0x92,
    0x73, 0x1a, 0xa4, 0xf8, 0x99, 0xf9, 0x41, 0xfd, 0xf3, 0x59, 0xc9, 0x0b,
    0x4e, 0x9c, 0x32, 0x3e, 0x8a, 0x28, 0x5c, 0x34, 0x35, 0xd7, 0xab, 0xec,
    0xd1, 0xbf, 0x6c, 0xb1, 0xa9, 0x51, 0x4a, 0xe0, 0x52, 0x46, 0x1e, 0x10,
    0xb6, 0x3c, 0xe8, 0x43, 0xa4, 0xb5, 0x4b, 0x96, 0x6a, 0xc3, 0xed, 0xab,
    0xbd, 0x77, 0xd8, 0x85, 0x56, 0x7a, 0xe6, 0x28, 0x91, 0xd7, 0x3c, 0xf3,
    0xea, 0x70, 0x57, 0x22, 0xe5, 0x26, 0xf4, 0x70, 0x33, 0x20, 0x81, 0x78,
    0xdc, 0xb1, 0x3a, 0x6a, 0x41, 0xbd, 0x13, 0xf1, 0x7d, 0xdd, 0x96, 0x0d,
    0x9b, 0x02, 0x03, 0x01, 0x00, 0x01,
};

and pass kPublicKey and sizeof(kPublicKey) into the function. We at least avoid
storing a base64-encoded string in the binary (smaller) and no need to pull in a
PEM parser.

If you like, you can call this kPublicKeyDER or kPublicKeySPKI to be explicit
about what it is. (It's a DER-encoded SubjectPublicKeyInfo. It's literally the
base64-decode of the PEM version. :-) )

[iclelland, 2015/12/22 05:45:28]

Thanks, done. I wanted something paste-able from an OpenSSL-generated private
key, but you're right that this will take up less space (code+data), and be
generally faster.

+
+/* By RFC 3447, the maximum salt length for RSAPSS is
+ * ceil((keySize-1)/8) - hashSize/8 - 2
+ */

[davidben, 2015/12/18 22:23:17]

Nit: This can use // for comments

[iclelland, 2015/12/22 05:45:28]

Done.

+const size_t kSaltLength = ((2048 + 6) >> 3) - (256 >> 3) - 2;

[davidben, 2015/12/18 22:23:16]

So, I'm not all that familiar with RSA-PSS, but I asked agl about salt length
guidance and he says:
"""
Equal to the hash length or something?
It's one of those cases where the spec is stupidly over general.
I don't think it really matters.
"""

QUIC seems to use the length of the hash, judging by ProofVerifierChromium.

[iclelland, 2015/12/22 05:45:28]

I used the max length, and ensured that this was interoperable with the Python
cryptography.hazmat package. I've replaced this with the constant `-2`, which,
as it turns out, implies the same calculation
(https://commondatastorage.googleapis.com/chromium-boringssl-docs/evp.h.html#E...).

If you prefer, though, I can reduce it to 256 bits to match the hash.

+
+}  // namespace
 
 namespace content {
 
@@ -59,8 +84,49 @@ ApiKey::ApiKey(const std::string& signature,
       expiry_timestamp_(expiry_timestamp) {}
 
 bool ApiKey::IsValidNow(const base::Time& now) const {
+  return ValidateDate(now) && ValidateSignature(kPublicKeyPEM);
+}
+
+bool ApiKey::ValidateDate(const base::Time& now) const {
   base::Time expiry_time = base::Time::FromDoubleT((double)expiry_timestamp_);
   return expiry_time > now;
 }
 
+bool ApiKey::ValidateSignature(const char* publicKeyPEM) const {

[davidben, 2015/12/18 22:23:16]

public_key_pem

[iclelland, 2015/12/22 05:45:28]

Done.

+  return ValidateSignature(signature_, data_, publicKeyPEM);
+}
+
+// static
+bool ApiKey::ValidateSignature(const std::string& signatureText,
+                               const std::string& data,
+                               const char* publicKeyPEM) {
+  std::string signature;
+  // signature is base64-encoded
+  if (!base::IsStringASCII(signatureText)) {

[davidben, 2015/12/18 22:23:16]

Does base::Base64Decode not check this for you?

[iclelland, 2015/12/22 05:45:28]

Yes. Yes I suppose it does, in a roundabout way (not to mention also filtering
out the other 63 invalid ASCII characters). Thanks :)

+    return false;
+  }
+  if (!base::Base64Decode(signatureText, &signature)) {
+    return false;
+  }
+
+  net::PEMTokenizer pem_tokenizer(publicKeyPEM, {"PUBLIC KEY"});

[davidben, 2015/12/18 22:23:17]

I don't thiiink we get initializer lists yet? (Hope we do soon!) But it doesn't
matter since we can avoid involving PEM in this at all. :-)

[iclelland, 2015/12/22 05:45:28]

Acknowledged. PEMTokenizer is gone.

+  if (!pem_tokenizer.GetNext()) {
+    NOTREACHED();
+  }
+  std::string publicKey = pem_tokenizer.data();

[davidben, 2015/12/18 22:23:16]

public_key

[iclelland, 2015/12/22 05:45:28]

Done.

+  std::string dataInUTF8 = data;

[davidben, 2015/12/18 22:23:17]

data_in_utf8, but it looks like you can just data. I'm guessing this is ported
over from Blink code that had to deal with WebString.

[iclelland, 2015/12/22 05:45:28]

It's ported from my original attempt at this code, which all lived in blink
(until I realized that it made more sense over here :) )

+  crypto::SignatureVerifier sv;

[davidben, 2015/12/18 22:23:17]

verifier

[iclelland, 2015/12/22 05:45:28]

Done.

+  // TODO(iclelland): Switch to SubjectPublicKeyInfo to determine hash algorithm
+  // https://crbug.com/570684

[davidben, 2015/12/18 22:23:17]

Commented on the bug, but this seems just fine. Also I'm not sure
SubjectPublicKeyInfo is quite what you want. :-)

[iclelland, 2015/12/22 05:45:28]

Removed, thanks :)

+  sv.VerifyInitRSAPSS(

[davidben, 2015/12/18 22:23:17]

Check for failure. Shouldn't happen, but still.

[iclelland, 2015/12/22 05:45:28]

Done.

+      crypto::SignatureVerifier::SHA256, crypto::SignatureVerifier::SHA256,
+      kSaltLength, reinterpret_cast<const uint8*>(signature.data()),

[davidben, 2015/12/18 22:23:17]

uint8_t for new code (I should go and fix //crypto's interfaces since that's
small...)

[iclelland, 2015/12/22 05:45:28]

Done.

+      signature.length(), reinterpret_cast<const uint8*>(publicKey.data()),
+      publicKey.length());
+  sv.VerifyUpdate(reinterpret_cast<const uint8*>(dataInUTF8.data()),
+                  dataInUTF8.length());
+  // TODO(iclelland): Support Key revocation through CRL
+  return sv.VerifyFinal();
+}
+
 }  // namespace