Add wc_SignCert_cb API for external signing callbacks #9632
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This pull request adds support for signing certificates and CSRs using a user-provided callback function, enabling integration with external signing devices (such as TPMs or HSMs) without relying on the crypto callback infrastructure. This is particularly useful for FIPS-compliant applications and scenarios where offloading cryptographic operations is required. The changes include new API definitions, documentation, internal implementation, and tests for the callback-based signing mechanism.
New Callback-Based Certificate Signing API
wc_SignCert_cbfunction and thewc_SignCertCbcallback type, allowing certificates and CSRs to be signed via an external callback for flexible integration with devices like TPMs/HSMs. [1] [2] [3]Internal Implementation
MakeSignatureCbfunction to handle hashing, digest encoding, and invoking the user-provided signing callback, supporting both RSA and ECC key types.Testing
Setup:
TPM simulator: swtpm running on port 2321
Built wolfSSL with: --enable-certgen --enable-certreq --enable-certext --enable-cryptocb
Built wolfTPM with: --enable-swtpm --enable-certgen --enable-debug
Tests Run:
Generated RSA and ECC test keys in TPM
Created CSRs using ./examples/csr/csr
Validated CSRs with openssl req -text -noout
Results:
wc_SignCert_cb compiled into wolfSSL
wolfTPM2_SignCertCb and CSR_MakeAndSign_Cb compiled into wolfTPM
Generated valid RSA (1228 bytes) and ECC (696 bytes) CSRs
CSRs verified successfully with OpenSSL