[PATCH v2 4/5] lib: mbedtls: sha256: add support of key derivation

[Philippe Reynes]

Adds the support of key derivation using the scheme hkdf.
This scheme is defined in rfc5869.

Signed-off-by: Philippe Reynes <philippe.rey...@softathome.com>
---
 include/u-boot/sha256.h |  5 +++++
 lib/mbedtls/sha256.c    | 18 ++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/include/u-boot/sha256.h b/include/u-boot/sha256.h
index 77dbcd4553a..0a6e309e3ab 100644
--- a/include/u-boot/sha256.h
+++ b/include/u-boot/sha256.h
@@ -48,4 +48,9 @@ void sha256_hmac(const unsigned char *key, int keylen,
                 const unsigned char *input, unsigned int ilen,
                 unsigned char *output);
 
+int sha256_hkdf(const unsigned char *salt, int saltlen,
+               const unsigned char *ikm, int ikmlen,
+               const unsigned char *info, int infolen,
+               unsigned char *output, int outputlen);
+
 #endif /* _SHA256_H */
diff --git a/lib/mbedtls/sha256.c b/lib/mbedtls/sha256.c
index 1b9fc1a8503..c38e3e5818c 100644
--- a/lib/mbedtls/sha256.c
+++ b/lib/mbedtls/sha256.c
@@ -11,6 +11,9 @@
 #include <string.h>
 #include <u-boot/sha256.h>
 
+#include <mbedtls/md.h>
+#include <mbedtls/hkdf.h>
+
 const u8 sha256_der_prefix[SHA256_DER_LEN] = {
        0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86,
        0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05,
@@ -98,3 +101,18 @@ void sha256_hmac(const unsigned char *key, int keylen,
        memset(tmpbuf, 0, sizeof(tmpbuf));
        memset(&ctx, 0, sizeof(sha256_context));
 }
+
+int sha256_hkdf(const unsigned char *salt, int saltlen,
+               const unsigned char *ikm, int ikmlen,
+               const unsigned char *info, int infolen,
+               unsigned char *output, int outputlen)
+{
+       const mbedtls_md_info_t *md;
+
+       md = mbedtls_md_info_from_type(MBEDTLS_MD_SHA256);
+
+       return mbedtls_hkdf(md, salt, saltlen,
+                           ikm, ikmlen,
+                           info, infolen,
+                           output, outputlen);
+}
-- 
2.25.1