libbb: refactor CNG hashing implementation

The existing CNG implementation relied on multiple features only
implemented in "newer" Windows versions. This new implementation does
not use the aforementioned features and is therefore compatible with
systems running Windows Vista or higher.

function                                             old     new   delta
.rdata                                             87112   87288    +176
hmac_peek_hash                                        80     208    +128
get_alg_handle                                         -      96     +96
algorithm_provider_hmac_cache                          -      48     +48
algorithm_provider_cache                               -      48     +48
alg_id_mappings                                        -      48     +48
sha512_begin                                          16      48     +32
sha384_begin                                          16      48     +32
sha256_begin                                          16      48     +32
sha1_begin                                            16      48     +32
md5_begin                                             16      32     +16
hmac_hash_v                                           48      64     +16
hmac_end                                              48      64     +16
hmac_blocks.constprop.0                               96     112     +16
__imp_BCryptOpenAlgorithmProvider                      -       8      +8
__imp_BCryptDuplicateHash                              -       8      +8
BCryptOpenAlgorithmProvider                            -       8      +8
BCryptDuplicateHash                                    -       8      +8
------------------------------------------------------------------------------
(add/remove: 8/0 grow/shrink: 10/0 up/down: 768/0)            Total: 768 bytes

1 files changed, 30 insertions, 21 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 09ebad1f6..1c75df523 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -290,11 +290,8 @@ PUSH_AND_SET_FUNCTION_VISIBILITY_TO_HIDDEN
 #if ENABLE_FEATURE_USE_CNG_API
 # include <bcrypt.h>
 
-// these work on Windows >= 10
-# define BCRYPT_HMAC_SHA1_ALG_HANDLE   ((BCRYPT_ALG_HANDLE) 0x000000a1)
-# define BCRYPT_HMAC_SHA256_ALG_HANDLE ((BCRYPT_ALG_HANDLE) 0x000000b1)
-# define sha1_begin_hmac BCRYPT_HMAC_SHA1_ALG_HANDLE
-# define sha256_begin_hmac BCRYPT_HMAC_SHA256_ALG_HANDLE
+# define sha1_begin_hmac (get_alg_handle(CNG_ALG_ID_SHA1, true))
+# define sha256_begin_hmac (get_alg_handle(CNG_ALG_ID_SHA256, true))
 #else
 # define sha1_begin_hmac sha1_begin
 # define sha256_begin_hmac sha256_begin
@@ -2388,28 +2385,37 @@ enum {
 };
 
 #if defined CONFIG_FEATURE_USE_CNG_API
-struct bcrypt_hash_ctx_t {
+enum cng_algorithm_identifier {
+        CNG_ALG_ID_MD5 = 0,
+        CNG_ALG_ID_SHA1 = 1,
+        CNG_ALG_ID_SHA256 = 2,
+        CNG_ALG_ID_SHA384 = 3,
+        CNG_ALG_ID_SHA512 = 4
+};
+BCRYPT_ALG_HANDLE get_alg_handle(enum cng_algorithm_identifier algorithm_identifier, bool hmac);
+
+typedef struct bcrypt_hash_ctx {
         void *handle;
         void *hash_obj;
         unsigned int output_size;
-};
-typedef struct bcrypt_hash_ctx_t md5_ctx_t;
-typedef struct bcrypt_hash_ctx_t sha1_ctx_t;
-typedef struct bcrypt_hash_ctx_t sha256_ctx_t;
-typedef struct bcrypt_hash_ctx_t sha384_ctx_t;
-typedef struct bcrypt_hash_ctx_t sha512_ctx_t;
+} bcrypt_hash_ctx_t;
+typedef struct bcrypt_hash_ctx md5_ctx_t;
+typedef struct bcrypt_hash_ctx sha1_ctx_t;
+typedef struct bcrypt_hash_ctx sha256_ctx_t;
+typedef struct bcrypt_hash_ctx sha384_ctx_t;
+typedef struct bcrypt_hash_ctx sha512_ctx_t;
 typedef struct sha3_ctx_t {
         uint64_t state[25];
         unsigned bytes_queued;
         unsigned input_block_bytes;
 } sha3_ctx_t;
-void md5_begin(struct bcrypt_hash_ctx_t *ctx) FAST_FUNC;
-void sha1_begin(struct bcrypt_hash_ctx_t *ctx) FAST_FUNC;
-void sha256_begin(struct bcrypt_hash_ctx_t *ctx) FAST_FUNC;
-void sha384_begin(struct bcrypt_hash_ctx_t *ctx) FAST_FUNC;
-void sha512_begin(struct bcrypt_hash_ctx_t *ctx) FAST_FUNC;
-void generic_hash(struct bcrypt_hash_ctx_t *ctx, const void *buffer, size_t len) FAST_FUNC;
-unsigned generic_end(struct bcrypt_hash_ctx_t *ctx, void *resbuf) FAST_FUNC;
+void md5_begin(struct bcrypt_hash_ctx *ctx) FAST_FUNC;
+void sha1_begin(struct bcrypt_hash_ctx *ctx) FAST_FUNC;
+void sha256_begin(struct bcrypt_hash_ctx *ctx) FAST_FUNC;
+void sha384_begin(struct bcrypt_hash_ctx *ctx) FAST_FUNC;
+void sha512_begin(struct bcrypt_hash_ctx *ctx) FAST_FUNC;
+void generic_hash(struct bcrypt_hash_ctx *ctx, const void *buffer, size_t len) FAST_FUNC;
+unsigned generic_end(struct bcrypt_hash_ctx *ctx, void *resbuf) FAST_FUNC;
 # define md5_hash generic_hash
 # define sha1_hash generic_hash
 # define sha256_hash generic_hash
@@ -2462,7 +2468,7 @@ unsigned sha3_end(sha3_ctx_t *ctx, void *resbuf) FAST_FUNC;
 void FAST_FUNC sha256_block(const void *in, size_t len, uint8_t hash[32]);
 /* TLS benefits from knowing that sha1 and sha256 share these. Give them "agnostic" names too */
 #if defined CONFIG_FEATURE_USE_CNG_API
-typedef struct bcrypt_hash_ctx_t md5sha_ctx_t;
+typedef struct bcrypt_hash_ctx md5sha_ctx_t;
 #define md5sha_hash generic_hash
 #define sha_end generic_end
 #else
@@ -2478,7 +2484,10 @@ typedef struct hmac_ctx {
         md5sha_ctx_t hashed_key_xor_opad;
 } hmac_ctx_t;
 #else
-typedef struct bcrypt_hash_ctx_t hmac_ctx_t;
+typedef struct hmac_ctx {
+        BCRYPT_ALG_HANDLE alg_handle;
+        bcrypt_hash_ctx_t hash_ctx;
+} hmac_ctx_t;
 #endif
 #define HMAC_ONLY_SHA256 (!ENABLE_FEATURE_TLS_SHA1)
 typedef void md5sha_begin_func(md5sha_ctx_t *ctx) FAST_FUNC;