diff --git a/Makefile b/Makefile
index bcfbd65..d1376e8 100644
--- a/Makefile
+++ b/Makefile
@@ -694,6 +694,10 @@
 $(eval $(call assert_numeric,ARM_ARCH_MINOR))
 $(eval $(call assert_numeric,BRANCH_PROTECTION))
 
+ifdef KEY_SIZE
+        $(eval $(call assert_numeric,KEY_SIZE))
+endif
+
 ifeq ($(filter $(SANITIZE_UB), on off trap),)
         $(error "Invalid value for SANITIZE_UB: can be one of on, off, trap")
 endif
diff --git a/drivers/auth/mbedtls/mbedtls_common.mk b/drivers/auth/mbedtls/mbedtls_common.mk
index 63e65bd..f34d3d0 100644
--- a/drivers/auth/mbedtls/mbedtls_common.mk
+++ b/drivers/auth/mbedtls/mbedtls_common.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2015-2018, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2015-2019, ARM Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -59,6 +59,16 @@
     endif
 endif
 
+ifeq (${TF_MBEDTLS_KEY_SIZE},)
+    ifneq ($(findstring rsa,${TF_MBEDTLS_KEY_ALG}),)
+	ifeq (${KEY_SIZE},)
+            TF_MBEDTLS_KEY_SIZE		:=	2048
+	else
+            TF_MBEDTLS_KEY_SIZE		:=	${KEY_SIZE}
+	endif
+    endif
+endif
+
 ifeq (${HASH_ALG}, sha384)
     TF_MBEDTLS_HASH_ALG_ID	:=	TF_MBEDTLS_SHA384
 else ifeq (${HASH_ALG}, sha512)
@@ -79,6 +89,7 @@
 
 # Needs to be set to drive mbed TLS configuration correctly
 $(eval $(call add_define,TF_MBEDTLS_KEY_ALG_ID))
+$(eval $(call add_define,TF_MBEDTLS_KEY_SIZE))
 $(eval $(call add_define,TF_MBEDTLS_HASH_ALG_ID))
 
 
diff --git a/drivers/auth/tbbr/tbbr_cot.c b/drivers/auth/tbbr/tbbr_cot.c
index da3631b..6dd4ae2 100644
--- a/drivers/auth/tbbr/tbbr_cot.c
+++ b/drivers/auth/tbbr/tbbr_cot.c
@@ -7,6 +7,7 @@
 #include <stddef.h>
 
 #include <platform_def.h>
+#include <drivers/auth/mbedtls/mbedtls_config.h>
 
 #include <drivers/auth/auth_mod.h>
 #if USE_TBBR_DEFS
@@ -19,7 +20,22 @@
 /*
  * Maximum key and hash sizes (in DER format)
  */
+#if TF_MBEDTLS_USE_RSA
+#if TF_MBEDTLS_KEY_SIZE == 1024
+#define PK_DER_LEN			162
+#elif TF_MBEDTLS_KEY_SIZE == 2048
 #define PK_DER_LEN			294
+#elif TF_MBEDTLS_KEY_SIZE == 3072
+#define PK_DER_LEN			422
+#elif TF_MBEDTLS_KEY_SIZE == 4096
+#define PK_DER_LEN			550
+#else
+#error "Invalid value for TF_MBEDTLS_KEY_SIZE"
+#endif
+#else
+#define PK_DER_LEN			294
+#endif
+
 #define HASH_DER_LEN			83
 
 /*
diff --git a/include/drivers/auth/mbedtls/mbedtls_config.h b/include/drivers/auth/mbedtls/mbedtls_config.h
index f7248f9..6e179bb 100644
--- a/include/drivers/auth/mbedtls/mbedtls_config.h
+++ b/include/drivers/auth/mbedtls/mbedtls_config.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015-2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -13,6 +13,11 @@
 #define TF_MBEDTLS_ECDSA		2
 #define TF_MBEDTLS_RSA_AND_ECDSA	3
 
+#define TF_MBEDTLS_USE_RSA (TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_RSA \
+		|| TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_RSA_AND_ECDSA)
+#define TF_MBEDTLS_USE_ECDSA (TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_ECDSA \
+		|| TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_RSA_AND_ECDSA)
+
 /*
  * Hash algorithms currently supported on mbed TLS libraries
  */
@@ -54,19 +59,14 @@
 
 #define MBEDTLS_PLATFORM_C
 
-#if (TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_ECDSA)
+#if TF_MBEDTLS_USE_ECDSA
 #define MBEDTLS_ECDSA_C
 #define MBEDTLS_ECP_C
 #define MBEDTLS_ECP_DP_SECP256R1_ENABLED
-#elif (TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_RSA)
+#endif
+#if TF_MBEDTLS_USE_RSA
 #define MBEDTLS_RSA_C
 #define MBEDTLS_X509_RSASSA_PSS_SUPPORT
-#elif (TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_RSA_AND_ECDSA)
-#define MBEDTLS_RSA_C
-#define MBEDTLS_X509_RSASSA_PSS_SUPPORT
-#define MBEDTLS_ECDSA_C
-#define MBEDTLS_ECP_C
-#define MBEDTLS_ECP_DP_SECP256R1_ENABLED
 #endif
 
 #define MBEDTLS_SHA256_C
@@ -80,11 +80,20 @@
 #define MBEDTLS_X509_CRT_PARSE_C
 
 /* MPI / BIGNUM options */
-#define MBEDTLS_MPI_WINDOW_SIZE              2
-#define MBEDTLS_MPI_MAX_SIZE               256
+#define MBEDTLS_MPI_WINDOW_SIZE			2
+
+#if TF_MBEDTLS_USE_RSA
+#if TF_MBEDTLS_KEY_SIZE <= 2048
+#define MBEDTLS_MPI_MAX_SIZE			256
+#else
+#define MBEDTLS_MPI_MAX_SIZE			512
+#endif
+#else
+#define MBEDTLS_MPI_MAX_SIZE			256
+#endif
 
 /* Memory buffer allocator options */
-#define MBEDTLS_MEMORY_ALIGN_MULTIPLE        8
+#define MBEDTLS_MEMORY_ALIGN_MULTIPLE		8
 
 #ifndef __ASSEMBLER__
 /* System headers required to build mbed TLS with the current configuration */
@@ -95,13 +104,17 @@
 /*
  * Determine Mbed TLS heap size
  * 13312 = 13*1024
- * 7168 = 7*1024
+ * 11264 = 11*1024
+ * 7168  = 7*1024
  */
-#if (TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_ECDSA) \
-	|| (TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_RSA_AND_ECDSA)
+#if TF_MBEDTLS_USE_ECDSA
 #define TF_MBEDTLS_HEAP_SIZE		U(13312)
-#elif (TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_RSA)
+#elif TF_MBEDTLS_USE_RSA
+#if TF_MBEDTLS_KEY_SIZE <= 2048
 #define TF_MBEDTLS_HEAP_SIZE		U(7168)
+#else
+#define TF_MBEDTLS_HEAP_SIZE		U(11264)
+#endif
 #endif
 
 #endif /* MBEDTLS_CONFIG_H */