fix: zeroize stack buffer containing private key in deterministic ECDSA#798
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ChakshuGupta13 wants to merge 1 commit into
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fix: zeroize stack buffer containing private key in deterministic ECDSA#798ChakshuGupta13 wants to merge 1 commit into
ChakshuGupta13 wants to merge 1 commit into
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In mbedtls_ecdsa_sign_det_restartable(), the local buffer data[] holds the raw private key d (via mbedtls_mpi_write_binary) for HMAC-DRBG seeding per RFC 6979. After use, the buffer was not cleared, leaving up to 66 bytes of key material on the stack. Add mbedtls_platform_zeroize(data, sizeof(data)) in the cleanup path, consistent with the practice in hmac_drbg.c and rsa.c which zeroize their sensitive local buffers. Signed-off-by: Chakshu Gupta <chakshugupta2000@gmail.com>
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Summary
In
mbedtls_ecdsa_sign_det_restartable(), the local stack bufferdata[2 * MBEDTLS_ECP_MAX_BYTES]holds the raw ECDSA private keyd(written viambedtls_mpi_write_binary()) for HMAC-DRBG seeding per RFC 6979. After use, the buffer is not cleared in the cleanup path, leaving up to 66 bytes of key material on the stack until overwritten by subsequent calls.Fix
Add
mbedtls_platform_zeroize(data, sizeof(data))to the cleanup path, beforembedtls_hmac_drbg_free().Rationale
This brings
ecdsa.cto parity with peer modules:hmac_drbg.c: zeroesK[],seed[],buf[]at cleanup (5 call sites)rsa.c: zeroesbuf[],mask[],lhash[]at cleanup (4 call sites)ecdsa.c: currently has zero uses ofmbedtls_platform_zeroizein the entire fileScope
Defense-in-depth hardening. The threat model (SECURITY.md) excludes direct local memory access, so this is not classified as a vulnerability fix — it is a missing cleanup consistent with existing project conventions.
Checklist
ChangeLog.d/zeroize-ecdsa-stack.txtdevelopmentbranch