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@ -23,11 +23,13 @@ This is a project to create a Hardware Security Module (HSM) with a Raspberry Pi
- DKEK n-of-m threshold scheme.
- USB/CCID support with OpenSC, openssl, etc.
- Extended APDU support.
- Private keys and certificates import from WKY or PKCS#12 files.[^2]
[^1]: PKCS11 modules (`pkcs11-tool` and `sc-tool`) do not support CMAC and key derivation. It must be processed through raw APDU command (`opensc-tool -s`).
[^2]: Imports are available via SCS3 tool, and only if the Pico HSM is previously initialized with a DKEK and the DKEK shares are available during the import process. See [SCS3](/doc/rsa_4096_support.md "SCS3") for more information.
## Security considerations
All secret keys (asymmetric and symmetric) are stored encrypted in the flash memory of the Raspberry Pico. DKEK is used as a 256 bit AES key to protect private and secret keys. Keys are never stored in RAM except for signature and decryption operations. All keys (including DKEK) are loaded and cleared every time to avoid potential flaws.
All secret keys (asymmetric and symmetric) are stored encrypted in the flash memory of the Raspberry Pico. DKEK is used as a 256 bit AES key to protect private and secret keys. Keys are never stored in RAM except for signature and decryption operations and only during the process. All keys (including DKEK) are loaded and cleared every time to avoid potential security flaws.
At the same time, DKEK is encrypted with doubled salted and hashed PIN. Also, the PIN is hashed in memory during the session. Hence, PIN is never stored in plain text neither in flash nor in memory. Note that PIN is conveyed from the host to the HSM in plain text if no secure channel is provided.
@ -80,6 +82,8 @@ For backup, restore and DKEK share management, check [doc/backup-and-restore.md]
For AES key generation, encryption and decryption, check [doc/aes.md](/doc/aes.md).
For 4096 bits RSA support, check [doc/rsa_4096_support.md](/doc/rsa_4096_support.md).
## Key generation time
Generating EC keys is almost instant. RSA keypair generation takes some time, specially for `2048` and `4096` bits.
@ -100,6 +104,8 @@ The way to communicate is exactly the same as with other cards, such as OpenPGP
For an advanced usage, see the docs and examples.
Pico HSM also supports SCS3 tool. See [SCS3](/doc/rsa_4096_support.md "SCS3") for more information.
### Important
OpenSC relies on PCSC driver, which reads a list (`Info.plist`) that contains a pair of VID/PID of supported readers. In order to be detectable, you must patch the UF2 binary (if you just downloaded from the [Release section](https://github.com/polhenarejos/pico-hsm/releases "Release section")) or configure the project with the proper VID/PID with `USB_VID` and `USB_PID` parameters in `CMake` (see [Build section](#build "Build section")). Note that you cannot distribute the patched/compiled binary if you do not own the VID/PID or have an explicit authorization.