Add support for ECDSA signatures

This adds support for key version 5 which is an EC key using the NIST
P-256 curve parameters. OTAs may be signed with these keys using the
ECDSA signature algorithm with SHA-256.

Change-Id: Id88672a3deb70681c78d5ea0d739e10f839e4567

1 files changed, 190 insertions, 0 deletions

diff --git a/asn1_decoder.cpp b/asn1_decoder.cpp
new file mode 100644
index 0000000..7280f74
--- /dev/null
+++ b/asn1_decoder.cpp
@@ -0,0 +1,190 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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.
+ */
+
+#include <stdint.h>
+#include <string.h>
+
+#include "asn1_decoder.h"
+
+
+typedef struct asn1_context {
+    size_t length;
+    uint8_t* p;
+    int app_type;
+} asn1_context_t;
+
+
+static const int kMaskConstructed = 0xE0;
+static const int kMaskTag = 0x7F;
+static const int kMaskAppType = 0x1F;
+
+static const int kTagOctetString = 0x04;
+static const int kTagOid = 0x06;
+static const int kTagSequence = 0x30;
+static const int kTagSet = 0x31;
+static const int kTagConstructed = 0xA0;
+
+asn1_context_t* asn1_context_new(uint8_t* buffer, size_t length) {
+    asn1_context_t* ctx = (asn1_context_t*) calloc(1, sizeof(asn1_context_t));
+    if (ctx == NULL) {
+        return NULL;
+    }
+    ctx->p = buffer;
+    ctx->length = length;
+    return ctx;
+}
+
+void asn1_context_free(asn1_context_t* ctx) {
+    free(ctx);
+}
+
+static inline int peek_byte(asn1_context_t* ctx) {
+    if (ctx->length <= 0) {
+        return -1;
+    }
+    return *ctx->p;
+}
+
+static inline int get_byte(asn1_context_t* ctx) {
+    if (ctx->length <= 0) {
+        return -1;
+    }
+    int byte = *ctx->p;
+    ctx->p++;
+    ctx->length--;
+    return byte;
+}
+
+static inline bool skip_bytes(asn1_context_t* ctx, size_t num_skip) {
+    if (ctx->length < num_skip) {
+        return false;
+    }
+    ctx->p += num_skip;
+    ctx->length -= num_skip;
+    return true;
+}
+
+static bool decode_length(asn1_context_t* ctx, size_t* out_len) {
+    int num_octets = get_byte(ctx);
+    if (num_octets == -1) {
+        return false;
+    }
+    if ((num_octets & 0x80) == 0x00) {
+        *out_len = num_octets;
+        return 1;
+    }
+    num_octets &= kMaskTag;
+    if ((size_t)num_octets >= sizeof(size_t)) {
+        return false;
+    }
+    size_t length = 0;
+    for (int i = 0; i < num_octets; ++i) {
+        int byte = get_byte(ctx);
+        if (byte == -1) {
+            return false;
+        }
+        length <<= 8;
+        length += byte;
+    }
+    *out_len = length;
+    return true;
+}
+
+/**
+ * Returns the constructed type and advances the pointer. E.g. A0 -> 0
+ */
+asn1_context_t* asn1_constructed_get(asn1_context_t* ctx) {
+    int type = get_byte(ctx);
+    if (type == -1 || (type & kMaskConstructed) != kTagConstructed) {
+        return NULL;
+    }
+    size_t length;
+    if (!decode_length(ctx, &length) || length > ctx->length) {
+        return NULL;
+    }
+    asn1_context_t* app_ctx = asn1_context_new(ctx->p, length);
+    app_ctx->app_type = type & kMaskAppType;
+    return app_ctx;
+}
+
+bool asn1_constructed_skip_all(asn1_context_t* ctx) {
+    int byte = peek_byte(ctx);
+    while (byte != -1 && (byte & kMaskConstructed) == kTagConstructed) {
+        skip_bytes(ctx, 1);
+        size_t length;
+        if (!decode_length(ctx, &length) || !skip_bytes(ctx, length)) {
+            return false;
+        }
+        byte = peek_byte(ctx);
+    }
+    return byte != -1;
+}
+
+int asn1_constructed_type(asn1_context_t* ctx) {
+    return ctx->app_type;
+}
+
+asn1_context_t* asn1_sequence_get(asn1_context_t* ctx) {
+    if ((get_byte(ctx) & kMaskTag) != kTagSequence) {
+        return NULL;
+    }
+    size_t length;
+    if (!decode_length(ctx, &length) || length > ctx->length) {
+        return NULL;
+    }
+    return asn1_context_new(ctx->p, length);
+}
+
+asn1_context_t* asn1_set_get(asn1_context_t* ctx) {
+    if ((get_byte(ctx) & kMaskTag) != kTagSet) {
+        return NULL;
+    }
+    size_t length;
+    if (!decode_length(ctx, &length) || length > ctx->length) {
+        return NULL;
+    }
+    return asn1_context_new(ctx->p, length);
+}
+
+bool asn1_sequence_next(asn1_context_t* ctx) {
+    size_t length;
+    if (get_byte(ctx) == -1 || !decode_length(ctx, &length) || !skip_bytes(ctx, length)) {
+        return false;
+    }
+    return true;
+}
+
+bool asn1_oid_get(asn1_context_t* ctx, uint8_t** oid, size_t* length) {
+    if (get_byte(ctx) != kTagOid) {
+        return false;
+    }
+    if (!decode_length(ctx, length) || *length == 0 || *length > ctx->length) {
+        return false;
+    }
+    *oid = ctx->p;
+    return true;
+}
+
+bool asn1_octet_string_get(asn1_context_t* ctx, uint8_t** octet_string, size_t* length) {
+    if (get_byte(ctx) != kTagOctetString) {
+        return false;
+    }
+    if (!decode_length(ctx, length) || *length == 0 || *length > ctx->length) {
+        return false;
+    }
+    *octet_string = ctx->p;
+    return true;
+}