NIST SP 800-108r1-upd1: KDF Counter Implementation

crypto/fipsmodule/bcm.c

@@ -114,6 +114,7 @@
 #include "evp/p_rsa.c"
 #include "hkdf/hkdf.c"
 #include "hmac/hmac.c"
+#include "kdf/kbkdf.c"
 #include "kdf/sskdf.c"
 #include "md4/md4.c"
 #include "md5/md5.c"

crypto/fipsmodule/kdf/internal.h

@@ -10,6 +10,8 @@
 #define SSKDF_MAX_INPUT_LEN (1 << 30)
 #define SSKDF_COUNTER_SIZE 4
 
+#define KBKDF_COUNTER_SIZE 4
+
 typedef struct {
   void *data;
 } sskdf_variant_ctx;

crypto/fipsmodule/kdf/kbkdf.c

@@ -0,0 +1,100 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0 OR ISC
+
+#include <openssl/kdf.h>
+#include "internal.h"
+
+int KBKDF_ctr_hmac(uint8_t *out_key, size_t out_len, const EVP_MD *digest,
+                   const uint8_t *secret, size_t secret_len,
+                   const uint8_t *info, size_t info_len) {
+  int ret = 0;
+
+  HMAC_CTX *hmac_ctx = NULL;
+
+  if (!out_key || out_len == 0 || !secret || secret_len == 0) {
+    goto err;
+  }
+
+  hmac_ctx = HMAC_CTX_new();
+  if (!hmac_ctx) {
+    goto err;
+  }
+
+  if (!HMAC_Init_ex(hmac_ctx, secret, secret_len, digest, NULL)) {
+    goto err;
+  }
+
+  // Determine the length of the output in bytes of a single invocation of the
+  // HMAC function.
+  size_t h_output_bytes = HMAC_size(hmac_ctx);
+  if (h_output_bytes == 0 || h_output_bytes > EVP_MAX_MD_SIZE) {
+    goto err;
+  }
+
+  if (out_len > SIZE_MAX - h_output_bytes) {
+    goto err;
+  }
+
+  // NIST.SP.800-108r1-upd1: Step 1:
+  // Determine how many output chunks are required to produce the requested
+  // output length |out_len|. This determines how many times the variant compute
+  // function will be called to output key material.
+  uint64_t n = ((uint64_t)out_len + (uint64_t)h_output_bytes - 1) /
+               (uint64_t)h_output_bytes;
+
+  // NIST.SP.800-108r1-upd1: Step 2:
+  // Verify that the number of output chunks does not exceed an unsigned 32-bit
+  // integer.
+  if (n > UINT32_MAX) {
+    goto err;
+  }
+
+  size_t done = 0;
+
+  for (uint32_t i = 0; i < n; i++) {
+    uint8_t out_key_i[EVP_MAX_MD_SIZE];
+    uint8_t counter[KBKDF_COUNTER_SIZE];
+    size_t todo;
+
+    // Increment the counter
+    CRYPTO_store_u32_be(&counter[0], i + 1);
+
+    uint32_t written;
+
+    // NIST.SP.800-108r1-upd1: Step 4a:
+    // K(i) := PRF(K_IN, [i] || FixedInfo)
+    // Note |hmac_ctx| has already been configured with the secret key
+    if (!HMAC_Init_ex(hmac_ctx, NULL, 0, NULL, NULL) ||
+        !HMAC_Update(hmac_ctx, &counter[0], KBKDF_COUNTER_SIZE) ||
+        !HMAC_Update(hmac_ctx, info, info_len) ||
+        !HMAC_Final(hmac_ctx, out_key_i, &written) ||
+        written != h_output_bytes) {
+      OPENSSL_cleanse(&out_key_i[0], EVP_MAX_MD_SIZE);
+      goto err;
+    }
+
+    // NIST.SP.800-108r1-upd1: Step 4b, Step 5
+    // result := result || K(i)
+    todo = h_output_bytes;
+    if (todo > out_len - done) {
+      todo = out_len - done;
+    }
+    OPENSSL_memcpy(out_key + done, out_key_i, todo);
+    done += todo;
+
+    // When we are finished clear the temporary buffer to cleanse key material
+    // from stack.
+    if (done == out_len) {
+      OPENSSL_cleanse(&out_key_i[0], EVP_MAX_MD_SIZE);
+    }
+  }
+
+  ret = 1;
+
+err:
+  if (ret <= 0 && out_key && out_len > 0) {
+    OPENSSL_cleanse(out_key, out_len);
+  }
+  HMAC_CTX_free(hmac_ctx);
+  return ret;
+}

crypto/fipsmodule/kdf/kdf_test.cc

@@ -112,3 +112,67 @@ TEST(SSKDFTest, HMACNegativeTests) {
   ASSERT_FALSE(SSKDF_hmac(out.data(), out.size(), EVP_sha256(), &secret[0], 0,
                           NULL, 0, NULL, 0));
 }
+
+TEST(KBKDFCounterTest, TestVectors) {
+  FileTestGTest(
+      "crypto/fipsmodule/kdf/test/kbkdf_counter.txt", [](FileTest *t) {
+        const EVP_MD *md;
+        std::string hash;
+        ASSERT_TRUE(t->GetAttribute(&hash, "HASH"));
+        if (hash == "SHA1") {
+          md = EVP_sha1();
+        } else if (hash == "SHA-224") {
+          md = EVP_sha224();
+        } else if (hash == "SHA-256") {
+          md = EVP_sha256();
+        } else if (hash == "SHA-384") {
+          md = EVP_sha384();
+        } else if (hash == "SHA-512") {
+          md = EVP_sha512();
+        } else {
+          FAIL() << "Unknown HASH=" + hash;
+        }
+
+        std::vector<uint8_t> secret, info, expect;
+
+        ASSERT_TRUE(t->GetBytes(&secret, "SECRET"));
+        if (t->HasAttribute("INFO")) {
+          ASSERT_TRUE(t->GetBytes(&info, "INFO"));
+        } else {
+          info = std::vector<uint8_t>(0);
+        }
+        ASSERT_TRUE(t->GetBytes(&expect, "EXPECT"));
+
+        std::vector<uint8_t> out(expect.size());
+
+        ASSERT_TRUE(KBKDF_ctr_hmac(out.data(), out.size(), md, secret.data(),
+                                   secret.size(), info.data(), info.size()));
+        ASSERT_EQ(Bytes(expect.data(), expect.size()),
+                  Bytes(out.data(), out.size()));
+      });
+}
+
+TEST(KBKDFCounterTest, NegativeTests) {
+  const uint8_t secret[16] = {0};
+  std::vector<uint8_t> out(16);
+
+  // NULL output
+  ASSERT_FALSE(KBKDF_ctr_hmac(NULL, out.size(), EVP_sha256(), &secret[0],
+                              sizeof(secret), NULL, 0));
+
+  // zero-length output
+  ASSERT_FALSE(KBKDF_ctr_hmac(out.data(), 0, EVP_sha256(), &secret[0],
+                              sizeof(secret), NULL, 0));
+
+  // NULL Digest
+  ASSERT_FALSE(KBKDF_ctr_hmac(out.data(), out.size(), NULL, &secret[0],
+                              sizeof(secret), NULL, 0));
+
+  // NULL secret
+  ASSERT_FALSE(KBKDF_ctr_hmac(out.data(), out.size(), EVP_sha256(), NULL,
+                              sizeof(secret), NULL, 0));
+
+  // zero-length secret
+  ASSERT_FALSE(KBKDF_ctr_hmac(out.data(), out.size(), EVP_sha256(), &secret[0],
+                              0, NULL, 0));
+}

crypto/fipsmodule/kdf/sskdf.c

@@ -177,7 +177,7 @@ static int sskdf_variant_hmac_compute(sskdf_variant_ctx *ctx, uint8_t *out,
 
   // NIST.SP.800-56Cr2: Step 6.2 HMAC-hash(salt, counter || secret || info)
   // Note: |variant_ctx->hmac_ctx| is already initalized with the salt during
-  // it's initial construction.
+  // its initial construction.
   if (!HMAC_Init_ex(variant_ctx->hmac_ctx, NULL, 0, NULL, NULL) ||
       !HMAC_Update(variant_ctx->hmac_ctx, &counter[0], SSKDF_COUNTER_SIZE) ||
       !HMAC_Update(variant_ctx->hmac_ctx, secret, secret_len) ||
@@ -224,10 +224,11 @@ static int SSKDF(const sskdf_variant *variant, sskdf_variant_ctx *ctx,
   }
 
   // NIST.SP.800-56Cr2 Step 1:
-  // Determine how many output chunks are required to produce the request output
-  // length |out_len|. This determines how many times the variant compute
+  // Determine how many output chunks are required to produce the requested
+  // output length |out_len|. This determines how many times the variant compute
   // function will be called to output key material.
-  uint64_t n = (out_len + h_output_bytes - 1) / h_output_bytes;
+  uint64_t n = ((uint64_t)out_len + (uint64_t)h_output_bytes - 1) /
+               (uint64_t)h_output_bytes;
 
   // NIST.SP.800-56Cr2 Step 2:
   // Verify that the number of output chunks does not exceed an unsigned 32-bit
@@ -259,8 +260,9 @@ static int SSKDF(const sskdf_variant *variant, sskdf_variant_ctx *ctx,
     }
 
     // NIST.SP.800-56Cr2: Step 6.3. Step 7, Step 8
-    // Combine the output from |out_key_i| with the output written to |out_key| so far.
-    // Ensure that we only copy |out_len| bytes in total from all chunks.
+    // Combine the output from |out_key_i| with the output written to |out_key|
+    // so far. Ensure that we only copy |out_len| bytes in total from all
+    // chunks.
     todo = h_output_bytes;
     if (todo > out_len - done) {
       todo = out_len - done;
@@ -278,6 +280,9 @@ static int SSKDF(const sskdf_variant *variant, sskdf_variant_ctx *ctx,
   ret = 1;
 
 err:
+  if (ret <= 0 && out_key && out_len > 0) {
+    OPENSSL_cleanse(out_key, out_len);
+  }
   return ret;
 }