On Mon Sep 18, 2023 at 5:18 PM EEST, David Gstir wrote: > Update the documentation for trusted and encrypted KEYS with DCP as new > trust source: > > - Describe security properties of DCP trust source > - Describe key usage > - Document blob format > > Co-developed-by: Richard Weinberger <rich...@nod.at> > Signed-off-by: Richard Weinberger <rich...@nod.at> > Co-developed-by: David Oberhollenzer <david.oberhollen...@sigma-star.at> > Signed-off-by: David Oberhollenzer <david.oberhollen...@sigma-star.at> > Signed-off-by: David Gstir <da...@sigma-star.at> > --- > .../security/keys/trusted-encrypted.rst | 85 +++++++++++++++++++ > 1 file changed, 85 insertions(+) > > diff --git a/Documentation/security/keys/trusted-encrypted.rst > b/Documentation/security/keys/trusted-encrypted.rst > index 9bc9db8ec651..4452070afbe9 100644 > --- a/Documentation/security/keys/trusted-encrypted.rst > +++ b/Documentation/security/keys/trusted-encrypted.rst > @@ -42,6 +42,14 @@ safe. > randomly generated and fused into each SoC at manufacturing time. > Otherwise, a common fixed test key is used instead. > > + (4) DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs) > + > + Rooted to a one-time programmable key (OTP) that is generally burnt > + in the on-chip fuses and is accessible to the DCP encryption engine > only. > + DCP provides two keys that can be used as root of trust: the OTP key > + and the UNIQUE key. Default is to use the UNIQUE key, but selecting > + the OTP key can be done via a module parameter (dcp_use_otp_key). > + > * Execution isolation > > (1) TPM > @@ -57,6 +65,12 @@ safe. > > Fixed set of operations running in isolated execution environment. > > + (4) DCP > + > + Fixed set of cryptographic operations running in isolated execution > + environment. Only basic blob key encryption is executed there. > + The actual key sealing/unsealing is done on main processor/kernel > space. > + > * Optional binding to platform integrity state > > (1) TPM > @@ -79,6 +93,11 @@ safe. > Relies on the High Assurance Boot (HAB) mechanism of NXP SoCs > for platform integrity. > > + (4) DCP > + > + Relies on Secure/Trusted boot process (called HAB by vendor) for > + platform integrity. > + > * Interfaces and APIs > > (1) TPM > @@ -94,6 +113,11 @@ safe. > > Interface is specific to silicon vendor. > > + (4) DCP > + > + Vendor-specific API that is implemented as part of the DCP crypto > driver in > + ``drivers/crypto/mxs-dcp.c``. > + > * Threat model > > The strength and appropriateness of a particular trust source for a > given > @@ -129,6 +153,13 @@ selected trust source: > CAAM HWRNG, enable CRYPTO_DEV_FSL_CAAM_RNG_API and ensure the device > is probed. > > + * DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs) > + > + The DCP hardware device itself does not provide a dedicated RNG > interface, > + so the kernel default RNG is used. SoCs with DCP like the i.MX6ULL do > have > + a dedicated hardware RNG that is independent from DCP which can be > enabled > + to back the kernel RNG. > + > Users may override this by specifying ``trusted.rng=kernel`` on the kernel > command-line to override the used RNG with the kernel's random number pool. > > @@ -231,6 +262,19 @@ Usage:: > CAAM-specific format. The key length for new keys is always in bytes. > Trusted Keys can be 32 - 128 bytes (256 - 1024 bits). > > +Trusted Keys usage: DCP > +----------------------- > + > +Usage:: > + > + keyctl add trusted name "new keylen" ring > + keyctl add trusted name "load hex_blob" ring > + keyctl print keyid > + > +"keyctl print" returns an ASCII hex copy of the sealed key, which is in > format > +specific to this DCP key-blob implementation. The key length for new keys is > +always in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits). > + > Encrypted Keys usage > -------------------- > > @@ -426,3 +470,44 @@ string length. > privkey is the binary representation of TPM2B_PUBLIC excluding the > initial TPM2B header which can be reconstructed from the ASN.1 octed > string length. > + > +DCP Blob Format > +--------------- > + > +The Data Co-Processor (DCP) provides hardware-bound AES keys using its > +AES encryption engine only. It does not provide direct key sealing/unsealing. > +To make DCP hardware encryption keys usable as trust source, we define > +our own custom format that uses a hardware-bound key to secure the sealing > +key stored in the key blob. > + > +Whenever a new trusted key using DCP is generated, we generate a random > 128-bit > +blob encryption key (BEK) and 128-bit nonce. The BEK and nonce are used to > +encrypt the trusted key payload using AES-128-GCM.
"When a new trusted key using DCP is created, a random 128-bit blob encryption key (BEK) and 128-bit nonce are generated." ... or along the lines. BR, Jarkko
