Refactor RSA key generation for WebCrypto's NSS implementation.

content/child/webcrypto/webcrypto_util.cc

Index: content/child/webcrypto/webcrypto_util.cc
diff --git a/content/child/webcrypto/webcrypto_util.cc b/content/child/webcrypto/webcrypto_util.cc
index 929b491c4481be4667fce86c11fa5ec2c586a663..8c28fda36c6c2b5cef9edd5d34a5421e03543b5a 100644
--- a/content/child/webcrypto/webcrypto_util.cc
+++ b/content/child/webcrypto/webcrypto_util.cc
@@ -17,6 +17,31 @@ namespace content {
 
 namespace webcrypto {
 
+namespace {
+
+// Converts a (big-endian) WebCrypto BigInteger, with or without leading zeros,
+// to unsigned int.
+bool BigIntegerToUint(const uint8_t* data,
+                      unsigned int data_size,
+                      unsigned int* result) {
+  // TODO(eroman): Fix handling of empty biginteger. http://crbug.com/373552
+  if (data_size == 0)
+    return false;
+
+  *result = 0;
+  for (size_t i = 0; i < data_size; ++i) {
+    size_t reverse_i = data_size - i - 1;
+
+    if (reverse_i >= sizeof(*result) && data[i])
+      return false;  // Too large for a uint.
+
+    *result |= data[i] << 8 * reverse_i;
+  }
+  return true;
+}
+
+}  // namespace
+
 // This function decodes unpadded 'base64url' encoded data, as described in
 // RFC4648 (http://www.ietf.org/rfc/rfc4648.txt) Section 5. To do this, first
 // change the incoming data to 'base64' encoding by applying the appropriate
@@ -249,6 +274,34 @@ Status CheckKeyCreationUsages(blink::WebCryptoKeyUsageMask all_possible_usages,
   return Status::Success();
 }
 
+Status GetRsaKeyGenParameters(
+    const blink::WebCryptoRsaHashedKeyGenParams* params,
+    unsigned int* public_exponent,
+    unsigned int* modulus_length_bits) {
+  *modulus_length_bits = params->modulusLengthBits();
+
+  // Limit key sizes to those supported by NSS:
+  //   * Multiple of 8 bits
+  //   * 256 bits to 16K bits
+  if (*modulus_length_bits < 256 || *modulus_length_bits > 16384 ||
+      (*modulus_length_bits % 8) != 0) {
+    return Status::ErrorGenerateRsaUnsupportedModulus();
+  }
+
+  if (!BigIntegerToUint(params->publicExponent().data(),
+                        params->publicExponent().size(),
+                        public_exponent)) {
+    return Status::ErrorGenerateKeyPublicExponent();
+  }
+
+  // OpenSSL hangs when given bad public exponents, whereas NSS simply fails. To
+  // avoid feeding OpenSSL data that will hang use a whitelist.
+  if (*public_exponent != 3 && *public_exponent != 65537)
+    return Status::ErrorGenerateKeyPublicExponent();
+
+  return Status::Success();
+}
+
 }  // namespace webcrypto
 
 }  // namespace content