build: Default to use TI degenerate key for signing on non-HS devices

Switch to using the TI degenerate key to sign the system firmware binary
image on GP devices during the image tree blob build process. Using this
key speeds up the time needed by the ROM code execution for processing
this image and with this shortens our boot time.

The previous default behavior of signing with a random key can still
be triggered by passing an empty KEY variable to the make command as
follows:

$ make KEY=""

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Reviewed-by: Suman Anna <s-anna@ti.com>

3 files changed, 22 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index 586873023..980a53f83 100644
--- a/Makefile
+++ b/Makefile
@@ -61,6 +61,8 @@ SYSFW_HS_INNER_CERT_DL_URL ?= https://git.ti.com/processor-firmware/ti-linux-fir
 # Set HS SYSFW image signing key
 ifdef HS
 KEY ?= $(TI_SECURE_DEV_PKG)/keys/custMpk.pem
+else
+KEY ?= ti-degenerate-key.pem
 endif
 
 CROSS_COMPILE ?= arm-linux-gnueabihf-
diff --git a/README.md b/README.md
index 35640117a..2c0d3141a 100644
--- a/README.md
+++ b/README.md
@@ -48,6 +48,16 @@ The default SYSFW image consumed by the build process is called
 using the **SYSFW_PATH** make variable. The build process will fail if the
 image can't be downloaded or no such file is provided.
 
+Further note by default the SYSFW image for use with general purpose (GP) devices
+(as opposed to high security devices) is signed with the TI degenerate key to
+optimize boot time (less processing time needed by ROM) but can also be signed
+with a random cryptoraphic key or another user-provided key. This signing behavior
+is controlled through the **KEY** make variable. Not explicitly setting **KEY**
+will result in the use of the TI degenerate key. To use a custom key populate the
+**KEY** variable to point to the key to get used. By clearing the default key
+setting by passing in **KEY=""** a random key will get generated and used during
+the build process.
+
 In order to download the SYSFW release image (if needed) and build the final
 **sysfw.itb** for consumption by U-Boot simply perform a make...
 
diff --git a/ti-degenerate-key.pem b/ti-degenerate-key.pem
new file mode 100644
index 000000000..bd7d3745a
--- /dev/null
+++ b/ti-degenerate-key.pem
@@ -0,0 +1,10 @@
+-----BEGIN RSA PRIVATE KEY-----
+MIIBWwIBAAKBgQDRfrnXQaP0k6vRK/gZ+bDflSU6y1JagGeQ/b+QYuiDz14japog
+8fRSu5WBsAxaSaySAUwS3L9Ppw+hGMecmyIJ494aMfZTtk1g49gU58joduiRnu7e
+QSZHMnehhuNlfD7A2tAAKnxIYuabs8zHYM/SS9Ne7t3kIQMbKfUSzNy6qQIBAQIB
+AQJBAOelUA376o6w3HkShXfN+shaOZYqFuTJ9exLMwsLp7DZKXB5F9I4JJ+Vkvho
+k6QWs7vkhleLSYUZknXHYm26ZE0CQQDnhTtd4PTBoZPjPXOeYMJFtEdMNy0XP6ey
+bcce389ugoY7BEkvASrd8PHgJQHziepgWOG4DGp33c64Hfq4zI3NAgEBAgEBAkA0
+RbK4uqoLciQluesTPU6lBy7Se3Dw0F9xBqlF5SR4KI6q+zQrHpBKyFOofMHZgizR
+iCrL55cxEM146zMw3AnF
+-----END RSA PRIVATE KEY-----