DeepCover Embedded Security in IoT: Public-key Secured Data Paths

Dependencies:   MaximInterface

The MAXREFDES155# is an internet-of-things (IoT) embedded-security reference design, built to authenticate and control a sensing node using elliptic-curve-based public-key cryptography with control and notification from a web server.

The hardware includes an ARM® mbed™ shield and attached sensor endpoint. The shield contains a DS2476 DeepCover® ECDSA/SHA-2 coprocessor, Wifi communication, LCD push-button controls, and status LEDs. The sensor endpoint is attached to the shield using a 300mm cable and contains a DS28C36 DeepCover ECDSA/SHA-2 authenticator, IR-thermal sensor, and aiming laser for the IR sensor. The MAXREFDES155# is equipped with a standard Arduino® form-factor shield connector for immediate testing using an mbed board such as the MAX32600MBED#. The combination of these two devices represent an IoT device. Communication to the web server is accomplished with the shield Wifi circuitry. Communication from the shield to the attached sensor module is accomplished over I2C . The sensor module represents an IoT endpoint that generates small data with a requirement for message authenticity/integrity and secure on/off operational control.

The design is hierarchical with each mbed platform and shield communicating data from the sensor node to a web server that maintains a centralized log and dispatches notifications as necessary. The simplicity of this design enables rapid integration into any star-topology IoT network to provide security with the low overhead and cost provided by the ECDSA-P256 asymmetric-key and SHA-256 symmetric-key algorithms.

More information about the MAXREFDES155# is available on the Maxim Integrated website.

Revision:
0:33d4e66780c0
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rapidjson/internal/dtoa.h	Fri Feb 24 11:23:12 2017 -0600
@@ -0,0 +1,245 @@
+// Tencent is pleased to support the open source community by making RapidJSON available.
+// 
+// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. All rights reserved.
+//
+// Licensed under the MIT License (the "License"); you may not use this file except
+// in compliance with the License. You may obtain a copy of the License at
+//
+// http://opensource.org/licenses/MIT
+//
+// Unless required by applicable law or agreed to in writing, software distributed 
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR 
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the 
+// specific language governing permissions and limitations under the License.
+
+// This is a C++ header-only implementation of Grisu2 algorithm from the publication:
+// Loitsch, Florian. "Printing floating-point numbers quickly and accurately with
+// integers." ACM Sigplan Notices 45.6 (2010): 233-243.
+
+#ifndef RAPIDJSON_DTOA_
+#define RAPIDJSON_DTOA_
+
+#include "itoa.h" // GetDigitsLut()
+#include "diyfp.h"
+#include "ieee754.h"
+
+RAPIDJSON_NAMESPACE_BEGIN
+namespace internal {
+
+#ifdef __GNUC__
+RAPIDJSON_DIAG_PUSH
+RAPIDJSON_DIAG_OFF(effc++)
+RAPIDJSON_DIAG_OFF(array-bounds) // some gcc versions generate wrong warnings https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59124
+#endif
+
+inline void GrisuRound(char* buffer, int len, uint64_t delta, uint64_t rest, uint64_t ten_kappa, uint64_t wp_w) {
+    while (rest < wp_w && delta - rest >= ten_kappa &&
+           (rest + ten_kappa < wp_w ||  /// closer
+            wp_w - rest > rest + ten_kappa - wp_w)) {
+        buffer[len - 1]--;
+        rest += ten_kappa;
+    }
+}
+
+inline unsigned CountDecimalDigit32(uint32_t n) {
+    // Simple pure C++ implementation was faster than __builtin_clz version in this situation.
+    if (n < 10) return 1;
+    if (n < 100) return 2;
+    if (n < 1000) return 3;
+    if (n < 10000) return 4;
+    if (n < 100000) return 5;
+    if (n < 1000000) return 6;
+    if (n < 10000000) return 7;
+    if (n < 100000000) return 8;
+    // Will not reach 10 digits in DigitGen()
+    //if (n < 1000000000) return 9;
+    //return 10;
+    return 9;
+}
+
+inline void DigitGen(const DiyFp& W, const DiyFp& Mp, uint64_t delta, char* buffer, int* len, int* K) {
+    static const uint32_t kPow10[] = { 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000 };
+    const DiyFp one(uint64_t(1) << -Mp.e, Mp.e);
+    const DiyFp wp_w = Mp - W;
+    uint32_t p1 = static_cast<uint32_t>(Mp.f >> -one.e);
+    uint64_t p2 = Mp.f & (one.f - 1);
+    unsigned kappa = CountDecimalDigit32(p1); // kappa in [0, 9]
+    *len = 0;
+
+    while (kappa > 0) {
+        uint32_t d = 0;
+        switch (kappa) {
+            case  9: d = p1 /  100000000; p1 %=  100000000; break;
+            case  8: d = p1 /   10000000; p1 %=   10000000; break;
+            case  7: d = p1 /    1000000; p1 %=    1000000; break;
+            case  6: d = p1 /     100000; p1 %=     100000; break;
+            case  5: d = p1 /      10000; p1 %=      10000; break;
+            case  4: d = p1 /       1000; p1 %=       1000; break;
+            case  3: d = p1 /        100; p1 %=        100; break;
+            case  2: d = p1 /         10; p1 %=         10; break;
+            case  1: d = p1;              p1 =           0; break;
+            default:;
+        }
+        if (d || *len)
+            buffer[(*len)++] = static_cast<char>('0' + static_cast<char>(d));
+        kappa--;
+        uint64_t tmp = (static_cast<uint64_t>(p1) << -one.e) + p2;
+        if (tmp <= delta) {
+            *K += kappa;
+            GrisuRound(buffer, *len, delta, tmp, static_cast<uint64_t>(kPow10[kappa]) << -one.e, wp_w.f);
+            return;
+        }
+    }
+
+    // kappa = 0
+    for (;;) {
+        p2 *= 10;
+        delta *= 10;
+        char d = static_cast<char>(p2 >> -one.e);
+        if (d || *len)
+            buffer[(*len)++] = static_cast<char>('0' + d);
+        p2 &= one.f - 1;
+        kappa--;
+        if (p2 < delta) {
+            *K += kappa;
+            int index = -static_cast<int>(kappa);
+            GrisuRound(buffer, *len, delta, p2, one.f, wp_w.f * (index < 9 ? kPow10[-static_cast<int>(kappa)] : 0));
+            return;
+        }
+    }
+}
+
+inline void Grisu2(double value, char* buffer, int* length, int* K) {
+    const DiyFp v(value);
+    DiyFp w_m, w_p;
+    v.NormalizedBoundaries(&w_m, &w_p);
+
+    const DiyFp c_mk = GetCachedPower(w_p.e, K);
+    const DiyFp W = v.Normalize() * c_mk;
+    DiyFp Wp = w_p * c_mk;
+    DiyFp Wm = w_m * c_mk;
+    Wm.f++;
+    Wp.f--;
+    DigitGen(W, Wp, Wp.f - Wm.f, buffer, length, K);
+}
+
+inline char* WriteExponent(int K, char* buffer) {
+    if (K < 0) {
+        *buffer++ = '-';
+        K = -K;
+    }
+
+    if (K >= 100) {
+        *buffer++ = static_cast<char>('0' + static_cast<char>(K / 100));
+        K %= 100;
+        const char* d = GetDigitsLut() + K * 2;
+        *buffer++ = d[0];
+        *buffer++ = d[1];
+    }
+    else if (K >= 10) {
+        const char* d = GetDigitsLut() + K * 2;
+        *buffer++ = d[0];
+        *buffer++ = d[1];
+    }
+    else
+        *buffer++ = static_cast<char>('0' + static_cast<char>(K));
+
+    return buffer;
+}
+
+inline char* Prettify(char* buffer, int length, int k, int maxDecimalPlaces) {
+    const int kk = length + k;  // 10^(kk-1) <= v < 10^kk
+
+    if (0 <= k && kk <= 21) {
+        // 1234e7 -> 12340000000
+        for (int i = length; i < kk; i++)
+            buffer[i] = '0';
+        buffer[kk] = '.';
+        buffer[kk + 1] = '0';
+        return &buffer[kk + 2];
+    }
+    else if (0 < kk && kk <= 21) {
+        // 1234e-2 -> 12.34
+        std::memmove(&buffer[kk + 1], &buffer[kk], static_cast<size_t>(length - kk));
+        buffer[kk] = '.';
+        if (0 > k + maxDecimalPlaces) {
+            // When maxDecimalPlaces = 2, 1.2345 -> 1.23, 1.102 -> 1.1
+            // Remove extra trailing zeros (at least one) after truncation.
+            for (int i = kk + maxDecimalPlaces; i > kk + 1; i--)
+                if (buffer[i] != '0')
+                    return &buffer[i + 1];
+            return &buffer[kk + 2]; // Reserve one zero
+        }
+        else
+            return &buffer[length + 1];
+    }
+    else if (-6 < kk && kk <= 0) {
+        // 1234e-6 -> 0.001234
+        const int offset = 2 - kk;
+        std::memmove(&buffer[offset], &buffer[0], static_cast<size_t>(length));
+        buffer[0] = '0';
+        buffer[1] = '.';
+        for (int i = 2; i < offset; i++)
+            buffer[i] = '0';
+        if (length - kk > maxDecimalPlaces) {
+            // When maxDecimalPlaces = 2, 0.123 -> 0.12, 0.102 -> 0.1
+            // Remove extra trailing zeros (at least one) after truncation.
+            for (int i = maxDecimalPlaces + 1; i > 2; i--)
+                if (buffer[i] != '0')
+                    return &buffer[i + 1];
+            return &buffer[3]; // Reserve one zero
+        }
+        else
+            return &buffer[length + offset];
+    }
+    else if (kk < -maxDecimalPlaces) {
+        // Truncate to zero
+        buffer[0] = '0';
+        buffer[1] = '.';
+        buffer[2] = '0';
+        return &buffer[3];
+    }
+    else if (length == 1) {
+        // 1e30
+        buffer[1] = 'e';
+        return WriteExponent(kk - 1, &buffer[2]);
+    }
+    else {
+        // 1234e30 -> 1.234e33
+        std::memmove(&buffer[2], &buffer[1], static_cast<size_t>(length - 1));
+        buffer[1] = '.';
+        buffer[length + 1] = 'e';
+        return WriteExponent(kk - 1, &buffer[0 + length + 2]);
+    }
+}
+
+inline char* dtoa(double value, char* buffer, int maxDecimalPlaces = 324) {
+    RAPIDJSON_ASSERT(maxDecimalPlaces >= 1);
+    Double d(value);
+    if (d.IsZero()) {
+        if (d.Sign())
+            *buffer++ = '-';     // -0.0, Issue #289
+        buffer[0] = '0';
+        buffer[1] = '.';
+        buffer[2] = '0';
+        return &buffer[3];
+    }
+    else {
+        if (value < 0) {
+            *buffer++ = '-';
+            value = -value;
+        }
+        int length, K;
+        Grisu2(value, buffer, &length, &K);
+        return Prettify(buffer, length, K, maxDecimalPlaces);
+    }
+}
+
+#ifdef __GNUC__
+RAPIDJSON_DIAG_POP
+#endif
+
+} // namespace internal
+RAPIDJSON_NAMESPACE_END
+
+#endif // RAPIDJSON_DTOA_