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Reduce stack usage in tls13_hkdf_expand

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Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7297)
This commit is contained in:
Bernd Edlinger 2018-09-23 09:20:54 +02:00
parent 7c69495712
commit ec0c5f5693
1 changed files with 12 additions and 4 deletions
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16
ssl/tls13_enc.c
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@ -13,7 +13,14 @@
#include <openssl/evp.h> #include <openssl/evp.h>
#include <openssl/kdf.h> #include <openssl/kdf.h>
#define TLS13_MAX_LABEL_LEN 246 /*
* RFC 8446, 7.1 Key Schedule, says:
* Note: With common hash functions, any label longer than 12 characters
* requires an additional iteration of the hash function to compute.
* The labels in this specification have all been chosen to fit within
* this limit.
*/
#define TLS13_MAX_LABEL_LEN 12
/* Always filled with zeros */ /* Always filled with zeros */
static const unsigned char default_zeros[EVP_MAX_MD_SIZE]; static const unsigned char default_zeros[EVP_MAX_MD_SIZE];
@ -29,14 +36,15 @@ int tls13_hkdf_expand(SSL *s, const EVP_MD *md, const unsigned char *secret,
const unsigned char *data, size_t datalen, const unsigned char *data, size_t datalen,
unsigned char *out, size_t outlen) unsigned char *out, size_t outlen)
{ {
const unsigned char label_prefix[] = "tls13 "; static const unsigned char label_prefix[] = "tls13 ";
EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL); EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL);
int ret; int ret;
size_t hkdflabellen; size_t hkdflabellen;
size_t hashlen; size_t hashlen;
/* /*
* 2 bytes for length of whole HkdfLabel + 1 byte for length of combined * 2 bytes for length of derived secret + 1 byte for length of combined
* prefix and label + bytes for the label itself + bytes for the hash * prefix and label + bytes for the label itself + 1 byte length of hash
* + bytes for the hash itself
*/ */
unsigned char hkdflabel[sizeof(uint16_t) + sizeof(uint8_t) + unsigned char hkdflabel[sizeof(uint16_t) + sizeof(uint8_t) +
+ sizeof(label_prefix) + TLS13_MAX_LABEL_LEN + sizeof(label_prefix) + TLS13_MAX_LABEL_LEN