mirror of
https://github.com/RfidResearchGroup/proxmark3.git
synced 2024-09-22 16:26:14 +08:00
131 lines
3.2 KiB
C
131 lines
3.2 KiB
C
/*
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* Not original to the mbedtls library. Taken from
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* https://github.com/mwarning/mbedtls_ecp_compression
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* to solve mbedtls' lack of support for elliptic point
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* compression and decompression
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*
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* Released under CC0 1.0 Universal License
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*/
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/*
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* This is all about mbedtls_ecp_decompress() and mbedtls_ecp_compress()
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*
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* Perform X25519 / Curve25519 point compression and decompression for mbedtls.
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* As of mbedtls 2.5.1, mbedtls does not support decompression yet.
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*
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*/
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#define MBEDTLS_ALLOW_PRIVATE_ACCESS
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#include "ecc_point_compression.h"
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int mbedtls_ecp_decompress(
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const mbedtls_ecp_group *grp,
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const unsigned char *input, size_t ilen,
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unsigned char *output, size_t *olen, size_t osize
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) {
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int ret;
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size_t plen;
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mbedtls_mpi r;
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mbedtls_mpi x;
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mbedtls_mpi n;
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plen = mbedtls_mpi_size(&grp->P);
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*olen = 2 * plen + 1;
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if (osize < *olen)
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return (MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL);
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if (ilen != plen + 1)
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return (MBEDTLS_ERR_ECP_BAD_INPUT_DATA);
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if (input[0] != 0x02 && input[0] != 0x03)
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return (MBEDTLS_ERR_ECP_BAD_INPUT_DATA);
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// output will consist of 0x04|X|Y
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memcpy(output, input, ilen);
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output[0] = 0x04;
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mbedtls_mpi_init(&r);
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mbedtls_mpi_init(&x);
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mbedtls_mpi_init(&n);
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// x <= input
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MBEDTLS_MPI_CHK(mbedtls_mpi_read_binary(&x, input + 1, plen));
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// r = x^2
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MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(&r, &x, &x));
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// r = x^2 + a
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if (grp->A.p == NULL) {
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// Special case where a is -3
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MBEDTLS_MPI_CHK(mbedtls_mpi_sub_int(&r, &r, 3));
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} else {
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MBEDTLS_MPI_CHK(mbedtls_mpi_add_mpi(&r, &r, &grp->A));
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}
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// r = x^3 + ax
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MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(&r, &r, &x));
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// r = x^3 + ax + b
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MBEDTLS_MPI_CHK(mbedtls_mpi_add_mpi(&r, &r, &grp->B));
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// Calculate square root of r over finite field P:
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// r = sqrt(x^3 + ax + b) = (x^3 + ax + b) ^ ((P + 1) / 4) (mod P)
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// n = P + 1
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MBEDTLS_MPI_CHK(mbedtls_mpi_add_int(&n, &grp->P, 1));
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// n = (P + 1) / 4
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MBEDTLS_MPI_CHK(mbedtls_mpi_shift_r(&n, 2));
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// r ^ ((P + 1) / 4) (mod p)
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MBEDTLS_MPI_CHK(mbedtls_mpi_exp_mod(&r, &r, &n, &grp->P, NULL));
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// Select solution that has the correct "sign" (equals odd/even solution in finite group)
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if ((input[0] == 0x03) != mbedtls_mpi_get_bit(&r, 0)) {
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// r = p - r
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MBEDTLS_MPI_CHK(mbedtls_mpi_sub_mpi(&r, &grp->P, &r));
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}
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// y => output
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ret = mbedtls_mpi_write_binary(&r, output + 1 + plen, plen);
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cleanup:
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mbedtls_mpi_free(&r);
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mbedtls_mpi_free(&x);
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mbedtls_mpi_free(&n);
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return (ret);
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}
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int mbedtls_ecp_compress(
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const mbedtls_ecp_group *grp,
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const unsigned char *input, size_t ilen,
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unsigned char *output, size_t *olen, size_t osize
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) {
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size_t plen;
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plen = mbedtls_mpi_size(&grp->P);
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*olen = plen + 1;
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if (osize < *olen)
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return (MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL);
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if (ilen != 2 * plen + 1)
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return (MBEDTLS_ERR_ECP_BAD_INPUT_DATA);
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if (input[0] != 0x04)
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return (MBEDTLS_ERR_ECP_BAD_INPUT_DATA);
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// output will consist of 0x0?|X
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memcpy(output, input, *olen);
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// Encode even/odd of Y into first byte (either 0x02 or 0x03)
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output[0] = 0x02 + (input[2 * plen] & 1);
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return (0);
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}
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