Add little endian export to Bignum
The function `mbedtls_mpi_write_binary()` writes big endian byte order,
but we need to be able to write little endian in some caseses. (For
example when handling keys corresponding to Montgomery curves.)
Used `echo xx | tac -rs ..` to transform the test data to little endian.
diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index 0727917..c4d7686 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -523,6 +523,24 @@
size_t buflen );
/**
+ * \brief Export X into unsigned binary data, little endian.
+ * Always fills the whole buffer, which will end with zeros
+ * if the number is smaller.
+ *
+ * \param X The source MPI. This must point to an initialized MPI.
+ * \param buf The output buffer. This must be a writable buffer of length
+ * \p buflen Bytes.
+ * \param buflen The size of the output buffer \p buf in Bytes.
+ *
+ * \return \c 0 if successful.
+ * \return #MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if \p buf isn't
+ * large enough to hold the value of \p X.
+ * \return Another negative error code on different kinds of failure.
+ */
+int mbedtls_mpi_write_binary_le( const mbedtls_mpi *X,
+ unsigned char *buf, size_t buflen );
+
+/**
* \brief Perform a left-shift on an MPI: X <<= count
*
* \param X The MPI to shift. This must point to an initialized MPI.
diff --git a/library/bignum.c b/library/bignum.c
index eb32640..f0882db 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -889,6 +889,45 @@
}
/*
+ * Export X into unsigned binary data, little endian
+ */
+int mbedtls_mpi_write_binary_le( const mbedtls_mpi *X,
+ unsigned char *buf, size_t buflen )
+{
+ size_t stored_bytes = X->n * ciL;
+ size_t bytes_to_copy;
+ size_t i;
+
+ if( stored_bytes < buflen )
+ {
+ bytes_to_copy = stored_bytes;
+ }
+ else
+ {
+ bytes_to_copy = buflen;
+
+ /* The output buffer is smaller than the allocated size of X.
+ * However X may fit if its leading bytes are zero. */
+ for( i = bytes_to_copy; i < stored_bytes; i++ )
+ {
+ if( GET_BYTE( X, i ) != 0 )
+ return( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL );
+ }
+ }
+
+ for( i = 0; i < bytes_to_copy; i++ )
+ buf[i] = GET_BYTE( X, i );
+
+ if( stored_bytes < buflen )
+ {
+ /* Write trailing 0 bytes */
+ memset( buf + stored_bytes, 0, buflen - stored_bytes );
+ }
+
+ return( 0 );
+}
+
+/*
* Export X into unsigned binary data, big endian
*/
int mbedtls_mpi_write_binary( const mbedtls_mpi *X,
diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index 7ad7ef6..f2be148 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -70,6 +70,15 @@
Test mbedtls_mpi_write_binary #2 (Buffer too small)
mbedtls_mpi_write_binary:16:"123123123123123123123123123":"23123123123123123123123123":13:MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
+Base test mbedtls_mpi_write_binary_le #1
+mbedtls_mpi_write_binary_le:10:"56125680981752282334141896320372489490613963693556392520816017892111350604111697682705498319512049040516698827829292076808006940873974979584527073481012636016353913462376755556720019831187364993587901952757307830896531678727717924":"24448b952fbbef93f89286ba330e62528b151eac265cc8ce3038519d09e148af89288e91f48b41acad55d9dc5e2b18097c106be4ce132721bf6359eaf403e7ff90623e8866ee5c192320418daa682f144adedf84f25de11f49d1fe009d374109":200:0
+
+Test mbedtls_mpi_write_binary_le #1 (Buffer just fits)
+mbedtls_mpi_write_binary_le:16:"123123123123123123123123123":"2331122331122331122331122301":14:0
+
+Test mbedtls_mpi_write_binary_le #2 (Buffer too small)
+mbedtls_mpi_write_binary_le:16:"123123123123123123123123123":"23311223311223311223311223":13:MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
+
Base test mbedtls_mpi_read_file #1
mbedtls_mpi_read_file:10:"data_files/mpi_10":"01f55332c3a48b910f9942f6c914e58bef37a47ee45cb164a5b6b8d1006bf59a059c21449939ebebfdf517d2e1dbac88010d7b1f141e997bd6801ddaec9d05910f4f2de2b2c4d714e2c14a72fc7f17aa428d59c531627f09":0
diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index 0ec45f6..5358379 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -378,6 +378,37 @@
}
/* END_CASE */
+/* BEGIN_CASE */
+void mbedtls_mpi_write_binary_le( int radix_X, char * input_X,
+ data_t * input_A, int output_size,
+ int result )
+{
+ mbedtls_mpi X;
+ unsigned char buf[1000];
+ size_t buflen;
+
+ memset( buf, 0x00, 1000 );
+
+ mbedtls_mpi_init( &X );
+
+ TEST_ASSERT( mbedtls_mpi_read_string( &X, radix_X, input_X ) == 0 );
+
+ buflen = mbedtls_mpi_size( &X );
+ if( buflen > (size_t) output_size )
+ buflen = (size_t) output_size;
+
+ TEST_ASSERT( mbedtls_mpi_write_binary_le( &X, buf, buflen ) == result );
+ if( result == 0)
+ {
+
+ TEST_ASSERT( hexcmp( buf, input_A->x, buflen, input_A->len ) == 0 );
+ }
+
+exit:
+ mbedtls_mpi_free( &X );
+}
+/* END_CASE */
+
/* BEGIN_CASE depends_on:MBEDTLS_FS_IO */
void mbedtls_mpi_read_file( int radix_X, char * input_file,
data_t * input_A, int result )