The set of signature schemes supported forms a part of the consensus rules for a Corda DLT network. Thus, it is important that implementations do not support pluggability of any crypto algorithms and do take measures to prevent algorithms supported by any underlying cryptography library from becoming accidentally accessible. Signing a transaction with an algorithm that is not a part of the base specification would result in a transaction being considered invalid by peer nodes and thus a loss of consensus occurring. The introduction of new algorithms over time will require a global upgrade of all nodes.
Corda has been designed to be cryptographically agile, in the sense that the available set of signature schemes is carefully selected based on various factors, such as provided security-level and cryptographic strength, compatibility with various HSM vendors, algorithm standardisation, variety of cryptographic primitives, business demand, option for post-quantum resistance, side channel security, efficiency and rigorous testing.
Before we present the pool of supported schemes it is useful to be familiar with Network certificates and API: Identity. An important design decision in Corda is its shared hierarchy between the TLS and Node Identity certificates.
A Corda network has 8 types of keys and a regular node requires 4 of them:
- The root network CA key
- The doorman CA key
- The network map key
- The service identity key(s) (per service, such as a notary cluster; it can be a Composite key)
- The node CA key(s) (one per node)
- The legal identity key(s) (one per node)
- The tls key(s) (per node)
- The confidential identity key(s) (per node)
We can visualise the certificate structure as follows (for a detailed description of cert-hierarchy, see Network certificates):
Due to the shared certificate hierarchy, the following 4 key/certificate types: root network CA, doorman CA, node CA and tls should be compatible with the standard TLS 1.2 protocol. The latter is a requirement from the TLS certificate-path validator. It is highlighted that the rest of the keys can be any of the 5 supported cipher suites. For instance, network map is ECDSA NIST P-256 (secp256r1) in the Corda Network (CN) as it is well-supported by the underlying HSM device, but the default for dev-mode is Pure EdDSA (ed25519).
The following table presents the 5 signature schemes currently supported by Corda. The TLS column shows which of them are compatible with TLS 1.2, while the default scheme per key type is also shown in the last column.
|Cipher suite||Description||TLS||Default for|
Pure EdDSA using the
EdDSA represents the current state of the art in mainstream
cryptography. It implements elliptic curve cryptography
with deterministic signatures a fast implementation,
explained constants, side channel resistance and many other
desirable characteristics. However, it is relatively new
and not widely supported, for example, you can’t use it in
TLS yet (a draft RFC exists but is not standardised yet).
ECDSA using the
NIST P-256 curve
This is the default choice for most systems that support
elliptic curve cryptography today and is recommended by
NIST. It is also supported by the majority of the HSM
ECDSA using the
Koblitz k1 curve
secp256k1 is the curve adopted by Bitcoin and as such there
is a wealth of infrastructure, code and advanced algorithms
designed for use with it. This curve is standardised by
NIST as part of the “Suite B” cryptographic algorithms and
as such is more widely supported than ed25519. By
supporting it we gain access to the ecosystem of advanced
cryptographic techniques and devices pioneered by the
RSA (3072bit) PKCS#1
RSA is well supported by any sort of hardware or software
as a signature algorithm no matter how old, for example,
legacy HSMs will support this along with obsolete operating
systems. RSA is using bigger keys than ECDSA and thus it is
recommended for inclusion only for its backwards
compatibility properties, and only for usage where legacy
constraints or government regulation forbids the usage of
more modern approaches.
SPHINCS-256 is a post-quantum secure algorithm that relies
only on hash functions. It is included as a hedge against
the possibility of a malicious adversary obtaining a
quantum computer capable of running Shor’s algorithm in
future. SPHINCS is based ultimately on a clever usage of
Merkle hash trees. Hash functions are a very heavily
studied and well understood area of cryptography. Thus, it
is assumed that there is a much lower chance of
breakthrough attacks on the underlying mathematical
problems. However, SPHINCS uses relatively big public keys,
it is slower and outputs bigger signatures than EdDSA,
ECDSA and RSA algorithms.