[SECNET RFC PATCH 1/5] hash: Put hash state on the caller's stack

[Ian Jackson]

This makes the code simpler too!

We rename len to slen, to distinguish hlen and slen (to help avoid
bugs where the wrong amount is allocated).

Signed-off-by: Ian Jackson <ijackson at chiark.greenend.org.uk>
---
 md5.c    | 15 ++++++---------
 rsa.c    |  9 +++++----
 secnet.h |  7 ++++---
 sha1.c   | 15 ++++++---------
 4 files changed, 21 insertions(+), 25 deletions(-)

diff --git a/md5.c b/md5.c
index 738d81a8..caaa5a68 100644
--- a/md5.c
+++ b/md5.c
@@ -238,14 +238,11 @@ MD5Transform(uint32_t buf[4], uint32_t const in[16])
 
 #endif
 
-static void *md5_init(void)
+static void md5_init(void *sst)
 {
-    struct MD5Context *ctx;
+    struct MD5Context *ctx=sst;
 
-    NEW(ctx);
     MD5Init(ctx);
-
-    return ctx;
 }
 
 static void md5_update(void *sst, const void *buf, int32_t len)
@@ -260,7 +257,6 @@ static void md5_final(void *sst, uint8_t *digest)
     struct MD5Context *ctx=sst;
 
     MD5Final(digest,ctx);
-    free(ctx);
 }
 
 struct md5 {
@@ -271,7 +267,6 @@ struct md5 {
 void md5_module(dict_t *dict)
 {
     struct md5 *st;
-    void *ctx;
     cstring_t testinput="12345\n";
     uint8_t expected[16]=
 	{0xd5,0x77,0x27,0x3f,0xf8,0x85,0xc3,0xf8,
@@ -284,14 +279,16 @@ void md5_module(dict_t *dict)
     st->cl.type=CL_HASH;
     st->cl.apply=NULL;
     st->cl.interface=&st->ops;
-    st->ops.len=16;
+    st->ops.hlen=16;
+    st->ops.slen=sizeof(struct MD5Context);
     st->ops.init=md5_init;
     st->ops.update=md5_update;
     st->ops.final=md5_final;
 
     dict_add(dict,"md5",new_closure(&st->cl));
 
-    ctx=md5_init();
+    uint8_t ctx[st->ops.slen];
+    md5_init(ctx);
     md5_update(ctx,testinput,strlen(testinput));
     md5_final(ctx,digest);
     for (i=0; i<16; i++) {
diff --git a/rsa.c b/rsa.c
index 81754a73..c87fcb76 100644
--- a/rsa.c
+++ b/rsa.c
@@ -77,7 +77,7 @@ static const char *hexchars="0123456789abcdef";
 static void rsa_sethash(struct rsacommon *c, struct hash_if *hash)
 {
     free(c->hashbuf);
-    c->hashbuf=safe_malloc(hash->len, "generate_msg");
+    c->hashbuf=safe_malloc(hash->hlen, "generate_msg");
     c->hashi=hash;
 }
 static void rsa_pub_sethash(void *sst, struct hash_if *hash)
@@ -92,7 +92,8 @@ static void rsa_priv_sethash(void *sst, struct hash_if *hash)
 }
 static void rsa_hash(struct rsacommon *c, const uint8_t *buf, int32_t len)
 {
-    void *hst=c->hashi->init();
+    uint8_t hst[c->hashi->slen];
+    c->hashi->init(hst);
     c->hashi->update(hst,buf,len);
     c->hashi->final(hst,c->hashbuf);
 }
@@ -158,7 +159,7 @@ static bool_t rsa_sign(void *sst, uint8_t *data, int32_t datalen,
 
     rsa_hash(&st->common,data,datalen);
     /* Construct the message representative. */
-    emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->common.hashi->len);
+    emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->common.hashi->hlen);
 
     /*
      * Produce an RSA signature (a^d mod n) using the Chinese
@@ -245,7 +246,7 @@ static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen,
     mpz_init(&c);
 
     rsa_hash(&st->common,data,datalen);
-    emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->common.hashi->len);
+    emsa_pkcs1(&st->n, &a, st->common.hashbuf, st->common.hashi->hlen);
 
     /* Terminate signature with a '0' - already checked that this will fit */
     int save = sig->sigstart[sig->siglen];
diff --git a/secnet.h b/secnet.h
index d2575f17..c6e8f496 100644
--- a/secnet.h
+++ b/secnet.h
@@ -643,11 +643,12 @@ struct dh_if {
 
 /* HASH interface */
 
-typedef void *hash_init_fn(void);
+typedef void hash_init_fn(void *st /* slen bytes alloc'd by caller */);
 typedef void hash_update_fn(void *st, const void *buf, int32_t len);
-typedef void hash_final_fn(void *st, uint8_t *digest);
+typedef void hash_final_fn(void *st, uint8_t *digest /* hlen bytes */);
 struct hash_if {
-    int32_t len; /* Hash output length in bytes */
+    int32_t slen; /* State length in bytes */
+    int32_t hlen; /* Hash output length in bytes */
     hash_init_fn *init;
     hash_update_fn *update;
     hash_final_fn *final;
diff --git a/sha1.c b/sha1.c
index 4cc63b5c..b11c25a6 100644
--- a/sha1.c
+++ b/sha1.c
@@ -287,14 +287,11 @@ unsigned char finalcount[8];
 /*************************************************************/
 
 /* Everything below here is the interface to secnet */
-static void *sha1_init(void)
+static void sha1_init(void *sst)
 {
-    SHA1_CTX *ctx;
+    SHA1_CTX *ctx=sst;
 
-    NEW(ctx);
     SHA1Init(ctx);
-
-    return ctx;
 }
 
 static void sha1_update(void *sst, const void *buf, int32_t len)
@@ -309,7 +306,6 @@ static void sha1_final(void *sst, uint8_t *digest)
     SHA1_CTX *ctx=sst;
 
     SHA1Final(digest,ctx);
-    free(ctx);
 }
 
 struct sha1 {
@@ -320,7 +316,6 @@ struct sha1 {
 void sha1_module(dict_t *dict)
 {
     struct sha1 *st;
-    void *ctx;
     cstring_t testinput="abcdbcdecdefdefgefghfghigh"
 	"ijhijkijkljklmklmnlmnomnopnopq";
     uint8_t expected[20]=
@@ -337,14 +332,16 @@ void sha1_module(dict_t *dict)
     st->cl.type=CL_HASH;
     st->cl.apply=NULL;
     st->cl.interface=&st->ops;
-    st->ops.len=20;
+    st->ops.hlen=20;
+    st->ops.slen=sizeof(SHA1_CTX);
     st->ops.init=sha1_init;
     st->ops.update=sha1_update;
     st->ops.final=sha1_final;
 
     dict_add(dict,"sha1",new_closure(&st->cl));
 
-    ctx=sha1_init();
+    uint8_t ctx[st->ops.slen];
+    sha1_init(ctx);
     sha1_update(ctx,testinput,strlen(testinput));
     sha1_final(ctx,digest);
     for (i=0; i<20; i++) {
-- 
2.11.0