Add EC key signing support

The DER encoded signature size of ECDSA with P-256 NIST CURVE is
nondeterministic for different input of sha256 hash. For example,
the signature size can be 70, 71, 72 bytes with the maximum
possible size of 72 bytes. However, we need the size of the
serialized signatures protobuf string to be fixed before signing;
because the size is part of the content to be signed.

To achieve that, we can add padding to the signature; and update the
definition of the signature proto to include the unpadded signature
size.
message Signatures {
  message Signature {
    optional uint32 version = 1;
    optional bytes data = 2;
    optional fixed32 unpadded_signature_size = 3;
  }
  repeated Signature signatures = 1;
}

Therefore the payload verifier will read the unpadded signature
and use it to verify against the public keys. For RSA signatures, the
signature data already has the correct size. So the legacy update_engine
on the old devices will still be able to verify these signatures in new
proto format.

We also need to update the version in signature proto, and the minor
version of update_engine.

The EC key in the unittest is generated with the command:
openssl ecparam -name prime256v1 -genkey -noout -out prime256v1-key.pem
openssl pkey -in prime256v1-key.pem -out unittest_key_EC.pem

Bug: 141244025
Test: unit tests pass, sign a package with EC key and and install on sailfish
Change-Id: I0a16c9f2f2c7fe9ccc1070c87fbbd6b94bc1f542

0 files changed, 0 insertions, 0 deletions