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68f1c20145
This commit enables the implementation of alternative mbedTLS cryptography functions, such as ECDSA sign and verify, in pure Python. Alternative functions are implemented in Python callbacks, that get invoked from wrapper functions when needed. The callback can return None to fall back to the default mbedTLS function. A common use case for this feature is with secure elements that have drivers implemented in Python. Currently, only the ECDSA alternate sign function wrapper is implemented. Tested signing with a private EC key stored on an NXP SE05x secure element. Signed-off-by: iabdalkader <i.abdalkader@gmail.com>
89 lines
3.0 KiB
C
89 lines
3.0 KiB
C
/*
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* This file is part of the MicroPython project, http://micropython.org/
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Copyright The Mbed TLS Contributors
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* Copyright (c) 2024 Damien P. George
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*
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* This file provides default fallback functions for use with alternate
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* cryptography functions implemented in Python.
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*/
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#if MICROPY_PY_SSL_ECDSA_SIGN_ALT
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#if defined(MBEDTLS_ECP_RESTARTABLE) || defined(MBEDTLS_ECDSA_DETERMINISTIC)
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#error "MICROPY_PY_SSL_ECDSA_SIGN_ALT cannot be used with MBEDTLS_ECP_RESTARTABLE or MBEDTLS_ECDSA_DETERMINISTIC"
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#endif
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#include <string.h>
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#define MBEDTLS_ALLOW_PRIVATE_ACCESS
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#include "mbedtls/platform.h"
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#include "mbedtls/ssl.h"
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#include "mbedtls/error.h"
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#include "mbedtls/ecdsa.h"
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#include "mbedtls/asn1write.h"
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extern int micropy_mbedtls_ecdsa_sign_alt(const mbedtls_mpi *d, const unsigned char *hash, size_t hlen,
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unsigned char *sig, size_t sig_size, size_t *slen);
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// Compute and write signature
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// See lib/mbedtls/library/ecdsa.c:688
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//
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// Note: To avoid duplicating a lot of code, MBEDTLS_ECDSA_SIGN_ALT is not defined,
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// which allows the default mbedtls_ecdsa_sign to be used as a fallback function.
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// However, mbedtls_ecdsa_sign cannot be wrapped because it is called internally
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// within its object file, so we wrap mbedtls_ecdsa_read/write_signature instead.
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int __wrap_mbedtls_ecdsa_write_signature(mbedtls_ecdsa_context *ctx,
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mbedtls_md_type_t md_alg,
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const unsigned char *hash, size_t hlen,
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unsigned char *sig, size_t sig_size, size_t *slen,
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int (*f_rng)(void *, unsigned char *, size_t),
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void *p_rng) {
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(void)md_alg;
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if (f_rng == NULL) {
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return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
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}
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// Check if curve is supported for ECDSA.
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if (!mbedtls_ecdsa_can_do(ctx->grp.id) || ctx->grp.N.p == NULL) {
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return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
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}
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// Try signing with the alternative function first.
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int ret = micropy_mbedtls_ecdsa_sign_alt(&ctx->d, hash, hlen, sig, sig_size, slen);
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// Fallback to the default mbedtls implementation if needed.
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if (ret == MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED) {
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mbedtls_mpi r, s;
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mbedtls_mpi_init(&r);
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mbedtls_mpi_init(&s);
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size_t len = 0;
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unsigned char buf[MBEDTLS_ECDSA_MAX_LEN] = { 0 };
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unsigned char *p = buf + sizeof(buf);
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MBEDTLS_MPI_CHK(mbedtls_ecdsa_sign(&ctx->grp, &r, &s, &ctx->d, hash, hlen, f_rng, p_rng));
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MBEDTLS_ASN1_CHK_CLEANUP_ADD(len, mbedtls_asn1_write_mpi(&p, buf, &s));
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MBEDTLS_ASN1_CHK_CLEANUP_ADD(len, mbedtls_asn1_write_mpi(&p, buf, &r));
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MBEDTLS_ASN1_CHK_CLEANUP_ADD(len, mbedtls_asn1_write_len(&p, buf, len));
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MBEDTLS_ASN1_CHK_CLEANUP_ADD(len, mbedtls_asn1_write_tag(&p, buf, MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE));
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if (len > sig_size) {
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ret = MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL;
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} else {
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ret = 0;
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*slen = len;
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memcpy(sig, p, len);
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}
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cleanup:
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mbedtls_mpi_free(&r);
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mbedtls_mpi_free(&s);
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}
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return ret;
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}
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#endif
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