TBB: add build option to save private keys

This patch adds a boolean build option 'SAVE_KEYS' to indicate the
certificate generation tool that it must save the private keys used
to establish the chain of trust. This option depends on 'CREATE_KEYS'
to be enabled. Default is '0' (do not save).

Because the same filenames are used as outputs to save the keys,
they are no longer a dependency to the cert_tool. This dependency
has been removed from the Makefile.

Documentation updated accordingly.

Change-Id: I67ab1c2b1f8a25793f0de95e8620ce7596a6bc3b

2 files changed, 24 insertions, 8 deletions

diff --git a/Makefile b/Makefile
index c33670b5..7f7ca8e7 100644
--- a/Makefile
+++ b/Makefile
@@ -73,6 +73,7 @@ DISABLE_PEDANTIC	:= 0
 # Flags to generate the Chain of Trust
 GENERATE_COT		:= 0
 CREATE_KEYS		:= 1
+SAVE_KEYS		:= 0
 # Flags to build TF with Trusted Boot support
 TRUSTED_BOARD_BOOT	:= 0
 AUTH_MOD		:= none
@@ -270,6 +271,7 @@ $(eval $(call add_define,USE_COHERENT_MEM))
 # Process Generate CoT flags
 $(eval $(call assert_boolean,GENERATE_COT))
 $(eval $(call assert_boolean,CREATE_KEYS))
+$(eval $(call assert_boolean,SAVE_KEYS))
 
 # Process TRUSTED_BOARD_BOOT flag
 $(eval $(call assert_boolean,TRUSTED_BOARD_BOOT))
@@ -327,6 +329,9 @@ ifneq (${GENERATE_COT},0)
 
     ifneq (${CREATE_KEYS},0)
         $(eval CRT_ARGS += -n)
+        ifneq (${SAVE_KEYS},0)
+            $(eval CRT_ARGS += -k)
+        endif
     endif
     $(eval CRT_ARGS += $(if ${ROT_KEY}, --rot-key ${ROT_KEY}))
     $(eval CRT_ARGS += $(if ${TRUSTED_WORLD_KEY}, --trusted-world-key ${TRUSTED_WORLD_KEY}))
@@ -514,7 +519,6 @@ $(eval FIP_ARGS += $(if $4,--bl$(1)-cert $(BUILD_PLAT)/bl$(1).crt))
 $(eval FIP_ARGS += $(if $4,$(if $5,--bl$(1)-key-cert $(BUILD_PLAT)/bl$(1)_key.crt)))
 
 $(eval CRT_DEPS += $(if $4,$(2),))
-$(eval CRT_DEPS += $(if $4,$(if $6,$(6),)))
 $(eval CRT_ARGS += $(if $4,--bl$(1) $(2)))
 $(eval CRT_ARGS += $(if $4,$(if $6,--bl$(1)-key $(6))))
 $(eval CRT_ARGS += $(if $4,--bl$(1)-cert $(BUILD_PLAT)/bl$(1).crt))
diff --git a/docs/user-guide.md b/docs/user-guide.md
index ef26f118..184e46ab 100644
--- a/docs/user-guide.md
+++ b/docs/user-guide.md
@@ -297,28 +297,40 @@ performed.
     certificate generation tool to create new keys in case no valid keys are
     present or specified. Allowed options are '0' or '1'. Default is '1'.
 
+*   `SAVE_KEYS`: This option is used when `GENERATE_COT=1`. It tells the
+    certificate generation tool to save the keys used to establish the Chain of
+    Trust. Allowed options are '0' or '1'. Default is '0' (do not save).
+
+    Note: This option depends on 'CREATE_KEYS' to be enabled. If the keys
+    already exist in disk, they will be overwritten without further notice.
+
 *   `ROT_KEY`: This option is used when `GENERATE_COT=1`. It specifies the
-    file that contains the ROT private key in PEM format.
+    file that contains the ROT private key in PEM format. If `SAVE_KEYS=1`, this
+    file name will be used to save the key.
 
 *   `TRUSTED_WORLD_KEY`: This option is used when `GENERATE_COT=1`. It
     specifies the file that contains the Trusted World private key in PEM
-    format.
+    format. If `SAVE_KEYS=1`, this file name will be used to save the key.
 
 *   `NON_TRUSTED_WORLD_KEY`: This option is used when `GENERATE_COT=1`. It
     specifies the file that contains the Non-Trusted World private key in PEM
-    format.
+    format. If `SAVE_KEYS=1`, this file name will be used to save the key.
 
 *   `BL30_KEY`: This option is used when `GENERATE_COT=1`. It specifies the
-    file that contains the BL3-0 private key in PEM format.
+    file that contains the BL3-0 private key in PEM format. If `SAVE_KEYS=1`,
+    this file name will be used to save the key.
 
 *   `BL31_KEY`: This option is used when `GENERATE_COT=1`. It specifies the
-    file that contains the BL3-1 private key in PEM format.
+    file that contains the BL3-1 private key in PEM format. If `SAVE_KEYS=1`,
+    this file name will be used to save the key.
 
 *   `BL32_KEY`: This option is used when `GENERATE_COT=1`. It specifies the
-    file that contains the BL3-2 private key in PEM format.
+    file that contains the BL3-2 private key in PEM format. If `SAVE_KEYS=1`,
+    this file name will be used to save the key.
 
 *   `BL33_KEY`: This option is used when `GENERATE_COT=1`. It specifies the
-    file that contains the BL3-3 private key in PEM format.
+    file that contains the BL3-3 private key in PEM format. If `SAVE_KEYS=1`,
+    this file name will be used to save the key.
 
 *   `PROGRAMMABLE_RESET_ADDRESS`: This option indicates whether the reset
     vector address can be programmed or is fixed on the platform. It can take