Command atcab_sha_hmac_init is failed with status 0xf4

[rrottmann]

I'm trying to generate a hmac digest. I am using slot 6 for this which is configured like this:

=========================  Slot: 6   ==================
Decoding SlotConfig value = 0x0F8F
Read key (except ECC private keys): 15
 If slot contains ECC private keys:
  External signatures of arbitrary messages are enabled: 1
  Internal signatures are enabled: 1
  ECDH operation is permitted for this key: 1
   ECDH master secret output mode: 1
NoMac bit: 0
LimitedUse bit: 0
EncryptRead bit: 0
IsSecret bit: 1
Write key: 15
Write config: 0x0 (hex) = 0000 (bin)
  Write cmd: Always
  DeriveKey cmd: Can't be used
  GenKey cmd: may NOT be used
  PrivWrite cmd: Forbidden
-------------
Decoding KeyConfig value = 0x007C
Private bit: 0
PubInfo bit: 0
KeyType: 7 [SHA or other]
Lockable bit: 1
ReqRandom bit: 1
ReqAuth bit: 0
AuthKey: 0
IntrusionDisable bit: 0
X509id: 0

The configuration zone is locked and I can interact with the i2c device.

Then I create a random key:

head -c 16 /dev/urandom > hmac.key

I can write the key (works only with less than 32 bytes):

atecc -b1 -c "hmac-write-key 6 0 hmac.key"
read key from file: Success

Then I try to digest a message:

echo "This is a test" > message
touch hmac.digest
# Usage: hmac-dgst <slot_id> <payload_file> <hmac_output>
atecc -b1 -c "hmac-dgst 6 message hmac.digest"
Command atcab_sha_hmac_init is failed with status 0xf4

Do I miss something? Is it necessary to lock the slot 6 before calculating the hmac? Is KeyType 7 [SHA or other] correct?

Thanks in advance for any pointers to get more familiar with atecc-util!

[evgeny-boger]

Could you please try the following patch:

diff --git a/atecc.c b/atecc.c
index 37312df..184d3ab 100644
--- a/atecc.c
+++ b/atecc.c
@@ -135,6 +135,7 @@ int main(int argc, char *argv[])
     ATCAIfaceCfg cfg = cfg_ateccx08a_i2c_default;
     cfg.atcai2c.bus = DEFAULT_I2C_BUS;
     cfg.atcai2c.slave_address = DEFAULT_I2C_SLAVE;
+    cfg.devtype = ATECC608A;
 
     while ((c = getopt(argc, argv, "h::c:b:s:vr:")) != -1) {
         switch (c) {

[evgeny-boger]

Is KeyType 7 [SHA or other] correct?

Yes

It works for me with the following slot config:

=========================  Slot: 7   ================== 
Decoding SlotConfig value = 0x4AC9
Read key (except ECC private keys): 9
 If slot contains ECC private keys:
  External signatures of arbitrary messages are enabled: 1
  Internal signatures are enabled: 0
  ECDH operation is permitted for this key: 0
   ECDH master secret output mode: 1
NoMac bit: 0
LimitedUse bit: 0
EncryptRead bit: 1
IsSecret bit: 1
Write key: 10
Write config: 0x4 (hex) = 0100 (bin)
  Write cmd: Encrypt
  DeriveKey cmd: Can't be used
  GenKey cmd: may NOT be used 
  PrivWrite cmd: Encrypt 
-------------
Decoding KeyConfig value = 0x003C
Private bit: 0
PubInfo bit: 0
KeyType: 7 [SHA or other]
Lockable bit: 1
ReqRandom bit: 0
ReqAuth bit: 0
AuthKey: 0
IntrusionDisable bit: 0
X509id: 0

[rrottmann]

Thanks for the quick response. Just tested this with current master. It still fails.
Please note that my ATECC608A is using i2c 0x35 and I set DEFAULT_I2C_SLAVE to 0x6A in config.h in order to talk to the device.

$ ./atecc -c serial
0123*********
$ head -c 16 /dev/urandom > hmac.key
$ atecc -b1 -c "hmac-write-key 6 0 hmac.key"
read key from file: Success
$ echo "This is a test" > message
$ touch hmac.digest
$ atecc -b1 -c "hmac-dgst 6 message hmac.digest"
Command atcab_sha_hmac_init is failed with status 0xf4
$ git diff
diff --git a/atecc.c b/atecc.c
index 744c322..d1514fe 100644
--- a/atecc.c
+++ b/atecc.c
@@ -136,6 +136,7 @@ int main(int argc, char *argv[])
     ATCAIfaceCfg cfg = cfg_ateccx08a_i2c_default;
     cfg.atcai2c.bus = DEFAULT_I2C_BUS;
     cfg.atcai2c.slave_address = DEFAULT_I2C_SLAVE;
+    cfg.devtype = ATECC608A;

     while ((c = getopt(argc, argv, "h::c:b:s:vr:")) != -1) {
         switch (c) {
diff --git a/config.h b/config.h
index 6fa7f00..6d4153e 100644
--- a/config.h
+++ b/config.h
@@ -1,6 +1,7 @@
 #pragma once

-#define DEFAULT_I2C_BUS 9
-#define DEFAULT_I2C_SLAVE 0xC0
+#define DEFAULT_I2C_BUS 1
+//#define DEFAULT_I2C_SLAVE 0xC0
+#define DEFAULT_I2C_SLAVE 0x6A

 #define MAX_CMDS 32

[webconn]

Hello,

Is that on purpose that ReqRandom bit is set to 1? As far as I remember, in this case ATECC chip requires nonce to be generated by internal RNG and this may be the reason for sha_hmac_init to fail.

[rrottmann]

Thanks for pointing me out the ReqRandom bit!

My first steps with ATECC608A were done with sample configs as it was difficult for a hobbyist without access to the complete datasheet to find a proper configuration.

The sample configures the device for multiple scenarios and there is another key slot without ReqRandom that I could use:

=========================  Slot: 8   ==================
Decoding SlotConfig value = 0x0F0F
Read key (except ECC private keys): 15
 If slot contains ECC private keys:
  External signatures of arbitrary messages are enabled: 1
  Internal signatures are enabled: 1
  ECDH operation is permitted for this key: 1
   ECDH master secret output mode: 1
NoMac bit: 0
LimitedUse bit: 0
EncryptRead bit: 0
IsSecret bit: 0
Write key: 15
Write config: 0x0 (hex) = 0000 (bin)
  Write cmd: Always
  DeriveKey cmd: Can't be used
  GenKey cmd: may NOT be used
  PrivWrite cmd: Forbidden
-------------
Decoding KeyConfig value = 0x003C
Private bit: 0
PubInfo bit: 0
KeyType: 7 [SHA or other]
Lockable bit: 1
ReqRandom bit: 0
ReqAuth bit: 0
AuthKey: 0
IntrusionDisable bit: 0
X509id: 0

Then I still needed Evgeny Bogers suggested patch to make it work. Without it, the following error occurs:

head -c 16 /dev/urandom > hmac.key
atecc -b1 -c "hmac-write-key 8 0 hmac.key"
#read key from file: Success
echo "This is a test" > message
touch hmac.digest
atecc -b1 -c "hmac-dgst 8 message hmac.digest"
#Command atcab_sha_hmac_finish is failed with status 210

[webconn]

Got it, thanks!

[evgeny-boger]

without access to the complete datasheet

I've been told that you can literally type "atecc608a complete datasheet" in Google to find one.

[webconn]

Then I still needed Evgeny Bogers suggested patch to make it work. Without it, the following error occurs:

head -c 16 /dev/urandom > hmac.key
atecc -b1 -c "hmac-write-key 8 0 hmac.key"
#read key from file: Success
echo "This is a test" > message
touch hmac.digest
atecc -b1 -c "hmac-dgst 8 message hmac.digest"
#Command atcab_sha_hmac_finish is failed with status 210

This issue will be fixed in PR #9.

[rrottmann]

@webconn Thanks for the fix. As my setup is still available, I've tested with a fresh clone of current master and it does not work for me.
Crosschecked with previous commit and suggested hardcoded devtype and this still works.

$ git diff
diff --git a/config.h b/config.h
index 6fa7f00..5d1e24e 100644
--- a/config.h
+++ b/config.h
@@ -1,6 +1,6 @@
 #pragma once

 #define DEFAULT_I2C_BUS 9
-#define DEFAULT_I2C_SLAVE 0xC0
+#define DEFAULT_I2C_SLAVE 0x6A

 #define MAX_CMDS 32
$ ./atecc -b1 -c "hmac-dgst 8 message hmac.digest"
Command atcab_info is failed with status e7
$ ./atecc -b1 -c serial
Command atcab_info is failed with status e7
$ git checkout d13c10ab1952ddd682429a77fcea39fa4d61d1ac
$ git diff
diff --git a/atecc.c b/atecc.c
index 744c322..d1514fe 100644
--- a/atecc.c
+++ b/atecc.c
@@ -136,6 +136,7 @@ int main(int argc, char *argv[])
     ATCAIfaceCfg cfg = cfg_ateccx08a_i2c_default;
     cfg.atcai2c.bus = DEFAULT_I2C_BUS;
     cfg.atcai2c.slave_address = DEFAULT_I2C_SLAVE;
+    cfg.devtype = ATECC608A;

     while ((c = getopt(argc, argv, "h::c:b:s:vr:")) != -1) {
         switch (c) {
diff --git a/config.h b/config.h
index 6fa7f00..5d1e24e 100644
--- a/config.h
+++ b/config.h
@@ -1,6 +1,6 @@
 #pragma once

 #define DEFAULT_I2C_BUS 9
-#define DEFAULT_I2C_SLAVE 0xC0
+#define DEFAULT_I2C_SLAVE 0x6A

 #define MAX_CMDS 32 
$ make clean && make
$ ./atecc -b1 -c "hmac-dgst 8 message hmac.digest"
$  xxd hmac.digest
#00000000: 2df4 f379 838b 30fc 27fb 5946 524f 87f2  -..y..0.'.YFRO..
#00000010: 1430 f9ce 47c4 d9da 2df1 5321 5837 8876  .0..G...-.S!X7.v

[evgeny-boger]

@rrottmann Thank you for the report.

Could you please post the output of
atecc -c info (only available in fresh master)
and
atecc -c 'dump-config -'

[rrottmann]

changes to current master

Used latest master and set my i2c slave id:

$ git rev-parse HEAD
1f08f086209788fdf8c0851f6dbd371918cf0f20
$ git diff
diff --git a/config.h b/config.h
index 6fa7f00..5d1e24e 100644
--- a/config.h
+++ b/config.h
@@ -1,6 +1,6 @@
 #pragma once

 #define DEFAULT_I2C_BUS 9
-#define DEFAULT_I2C_SLAVE 0xC0
+#define DEFAULT_I2C_SLAVE 0x6A

 #define MAX_CMDS 32

atecc -c info

$ ./atecc -b1 -c info
Found ATECC608A

atecc -c 'dump-config -'

https://pastebin.com/raw/QqJ6Yy2r