[PATCH v3 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.reynes at softathome.com>
---
 include/u-boot/sha256.h |  7 +++++++
 lib/mbedtls/sha256.c    | 22 ++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/include/u-boot/sha256.h b/include/u-boot/sha256.h
index 2f12275b703..5643efcb85c 100644
--- a/include/u-boot/sha256.h
+++ b/include/u-boot/sha256.h
@@ -49,4 +49,11 @@ void sha256_hmac(const unsigned char *key, int keylen,
 		 const unsigned char *input, unsigned int ilen,
 		 unsigned char *output);
 
+#if defined(CONFIG_HKDF_MBEDTLS)
+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
+
 #endif /* _SHA256_H */
diff --git a/lib/mbedtls/sha256.c b/lib/mbedtls/sha256.c
index 1b9fc1a8503..6e9659d31bb 100644
--- a/lib/mbedtls/sha256.c
+++ b/lib/mbedtls/sha256.c
@@ -11,6 +11,11 @@
 #include <string.h>
 #include <u-boot/sha256.h>
 
+#if CONFIG_IS_ENABLED(HKDF_MBEDTLS)
+#include <mbedtls/md.h>
+#include <mbedtls/hkdf.h>
+#endif
+
 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 +103,20 @@ void sha256_hmac(const unsigned char *key, int keylen,
 	memset(tmpbuf, 0, sizeof(tmpbuf));
 	memset(&ctx, 0, sizeof(sha256_context));
 }
+
+#if CONFIG_IS_ENABLED(HKDF_MBEDTLS)
+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);
+}
+#endif
-- 
2.25.1