Add initial crypto functionality

[libcontrac.git] / src / dtk.c

diff --git a/src/dtk.c b/src/dtk.c
new file mode 100644 (file)
index 0000000..3febd9f
--- /dev/null
+++ b/src/dtk.c
@@ -0,0 +1,139 @@
+/** \ingroup contrac
+ * @file
+ * @author     David Llewellyn-Jones
+ * @version    $(VERSION)
+ *
+ * @section LICENSE
+ *
+ *
+ *
+ * @brief
+ * @section DESCRIPTION
+ *
+ *
+ *
+ */
+
+// Includes
+
+#include <stdlib.h>
+#include <string.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#include <openssl/crypto.h>
+#include <openssl/kdf.h>
+#include <openssl/err.h>
+#include <openssl/evp.h>
+
+#include "contrac/contrac.h"
+#include "contrac/utils.h"
+#include "contrac/log.h"
+
+#include "contrac/dtk.h"
+
+// Defines
+
+#define DTK_INFO_PREFIX "CT-DTK"
+
+// Structures
+
+struct _Dtk {
+       // Daily key
+       unsigned char dtk[DTK_SIZE];
+       uint32_t day_number;
+};
+
+// Function prototypes
+
+// Function definitions
+
+Dtk * dtk_new() {
+       Dtk * data;
+       
+       data = calloc(sizeof(Dtk), 1);
+
+       return data;
+}
+
+void dtk_delete(Dtk * data) {
+       if (data) {
+               // Clear the data for security
+               memset(data, 0, sizeof(Dtk));
+
+               free(data);
+       }
+}
+
+bool contrac_generate_daily_key(Dtk * data, Contrac const * contrac, uint32_t day_number) {
+       int result = 1;
+       char encode[sizeof(DTK_INFO_PREFIX) + sizeof(day_number)];
+       size_t out_length = 0;
+       EVP_PKEY_CTX *pctx = NULL;
+       const unsigned char * tk;
+
+       // dtk_i <- HKDF(tk, NULL, (UTF8("CT-DTK") || D_i), 16)
+
+       if (result > 0) {
+               // Produce Info sequence UTF8("CT-DTK") || D_i)
+               // From the spec it's not clear whether this is string or byte concatenation.
+               // Here we use byte, but it might have to be changed
+               memcpy(encode, DTK_INFO_PREFIX, sizeof(DTK_INFO_PREFIX));
+               ((uint32_t *)(encode + sizeof(DTK_INFO_PREFIX)))[0] = day_number;
+
+               pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL);
+
+               result = EVP_PKEY_derive_init(pctx);
+       }
+
+       if (result > 0) {
+               result = EVP_PKEY_CTX_set_hkdf_md(pctx, EVP_sha256());
+       }
+
+       if (result > 0) {
+               result = EVP_PKEY_CTX_set1_hkdf_salt(pctx, NULL, 4);
+       }
+       
+       if (result > 0) {
+               tk = contrac_get_tracing_key(contrac);
+               result = EVP_PKEY_CTX_set1_hkdf_key(pctx, tk, TK_SIZE);
+       }
+       
+       if (result > 0) {
+               result = EVP_PKEY_CTX_add1_hkdf_info(pctx, encode, sizeof(encode));
+       }
+       
+       if (result > 0) {
+               out_length = DTK_SIZE;
+               result = EVP_PKEY_derive(pctx, data->dtk, &out_length);
+       }
+       
+       if ((result > 0) && (out_length == DTK_SIZE)) {
+               data->day_number = day_number;
+               result = 1;
+       }
+
+       if (result <= 0) {
+               LOG(LOG_ERR, "Error generating daily key: %lu\n", ERR_get_error());
+       }
+       
+       // Freeing a NULL value is safe
+       EVP_PKEY_CTX_free(pctx);
+
+       return (result > 0);
+}
+
+const unsigned char * dtk_get_daily_key(Dtk const * data) {
+       return data->dtk;
+}
+
+uint32_t dtk_get_day_number(Dtk const * data) {
+       return data->day_number;
+}
+
+void dtk_assign(Dtk * data, unsigned char const * dtk_bytes, uint32_t day_number) {
+       memcpy(data->dtk, dtk_bytes, DTK_SIZE);
+       data->day_number = day_number;
+}
+
+