Protection measures and security strategy
UM2262
34/94
UM2262 Rev 6
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PCROP
(proprietary code readout protection): a section of Flash is defined as execute-
only applying PCROP protection on it: it is not possible to access this section in reading
nor writing. Being an execute-only area, a key is protected with PCROP only if it is
"embedded" in a piece of code: executing this code moves the key to a specific pointer
in RAM. Placed behind the firewall, its execution is not possible from outside.
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WRP
(write protection): write protection is used to protect trusted code from external
attacks or even internal modifications such as unwanted writings/erase operations on
critical code/data.
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MPU
(memory protection unit): the MPU is used to make an embedded system more
robust by splitting the memory map for Flash and SRAMs into regions having their own
access rights. In the SBSFU application example, MPU is configured in order to ensure
that no other code is executed from any memories during SBSFU code execution.
When leaving the SBSFU application, the MPU configuration is updated to authorize
also the execution of user application code.
STSAFE-A Secure Element protections
The STSAFE-A100 is a highly secure solution with a secure operating system running on
the latest generation of secure microcontrollers:
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Security features
: The chip is CC EAL5+ AVA_VAN5 Common Criteria certified and
provides the following protections.
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Active shield
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Monitoring of environmental parameters
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Protection mechanism against faults
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Unique serial number on each die
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Protection against side-channel attacks
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Secure operating system
: STSAFE-A100 runs a secure operating system offering
protection against logical and physical attacks.
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Secure channel and device binding
: STSAFE-A100 allows a secure channel to be
set up with the STM32 in order to prevent eavesdropping of sensitive information on
the I²C line and to ensure pairing of a specific STM32 with a specific STSAFE-A100 (to
prevent cloning).
The secure channel is based on symmetric cryptography: two AES 128-bit keys (the so-
called host pairing keys) are used to implement services such as command authorization,
command data encryption, response data encryption and response authentication.