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[crypto] Add an abstraction of an elliptic curve

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Define an abstraction of an elliptic curve with a fixed generator and
one supported operation (scalar multiplication of a curve point).

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2024-01-30 13:26:36 +00:00
parent 27398f1360
commit 17135c83fb
3 changed files with 57 additions and 0 deletions
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31
src/crypto/x25519.c
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@@ -61,6 +61,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
#include <assert.h> #include <assert.h>
#include <errno.h> #include <errno.h>
#include <ipxe/init.h> #include <ipxe/init.h>
#include <ipxe/crypto.h>
#include <ipxe/x25519.h> #include <ipxe/x25519.h>
/** X25519 reduction constant /** X25519 reduction constant
@@ -300,6 +301,11 @@ static const uint8_t x25519_121665_raw[] = { 0x01, 0xdb, 0x41 };
/** Constant 121665 (used in the Montgomery ladder) */ /** Constant 121665 (used in the Montgomery ladder) */
static union x25519_oct258 x25519_121665; static union x25519_oct258 x25519_121665;
/** Constant g=9 (the group generator) */
static struct x25519_value x25519_generator = {
.raw = { 9, }
};
/** /**
* Initialise constants * Initialise constants
* *
@@ -811,3 +817,28 @@ int x25519_key ( const struct x25519_value *base,
/* Fail if result was all zeros (as required by RFC8422) */ /* Fail if result was all zeros (as required by RFC8422) */
return ( bigint_is_zero ( &point.value ) ? -EPERM : 0 ); return ( bigint_is_zero ( &point.value ) ? -EPERM : 0 );
} }
/**
* Multiply scalar by curve point
*
* @v base Base point (or NULL to use generator)
* @v scalar Scalar multiple
* @v result Result point to fill in
* @ret rc Return status code
*/
static int x25519_curve_multiply ( const void *base, const void *scalar,
void *result ) {
/* Use base point if applicable */
if ( ! base )
base = &x25519_generator;
return x25519_key ( base, scalar, result );
}
/** X25519 elliptic curve */
struct elliptic_curve x25519_curve = {
.name = "x25519",
.keysize = sizeof ( struct x25519_value ),
.multiply = x25519_curve_multiply,
};

23
src/include/ipxe/crypto.h
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@@ -195,6 +195,23 @@ struct pubkey_algorithm {
const void *public_key, size_t public_key_len ); const void *public_key, size_t public_key_len );
}; };
/** An elliptic curve */
struct elliptic_curve {
/** Curve name */
const char *name;
/** Key size */
size_t keysize;
/** Multiply scalar by curve point
*
* @v base Base point (or NULL to use generator)
* @v scalar Scalar multiple
* @v result Result point to fill in
* @ret rc Return status code
*/
int ( * multiply ) ( const void *base, const void *scalar,
void *result );
};
static inline void digest_init ( struct digest_algorithm *digest, static inline void digest_init ( struct digest_algorithm *digest,
void *ctx ) { void *ctx ) {
digest->init ( ctx ); digest->init ( ctx );
@@ -302,6 +319,12 @@ static inline int pubkey_match ( struct pubkey_algorithm *pubkey,
public_key_len ); public_key_len );
} }
static inline int elliptic_multiply ( struct elliptic_curve *curve,
const void *base, const void *scalar,
void *result ) {
return curve->multiply ( base, scalar, result );
}
extern void digest_null_init ( void *ctx ); extern void digest_null_init ( void *ctx );
extern void digest_null_update ( void *ctx, const void *src, size_t len ); extern void digest_null_update ( void *ctx, const void *src, size_t len );
extern void digest_null_final ( void *ctx, void *out ); extern void digest_null_final ( void *ctx, void *out );

3
src/include/ipxe/x25519.h
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@@ -11,6 +11,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
#include <stdint.h> #include <stdint.h>
#include <ipxe/bigint.h> #include <ipxe/bigint.h>
#include <ipxe/crypto.h>
/** X25519 unsigned big integer size /** X25519 unsigned big integer size
* *
@@ -88,4 +89,6 @@ extern int x25519_key ( const struct x25519_value *base,
const struct x25519_value *scalar, const struct x25519_value *scalar,
struct x25519_value *result ); struct x25519_value *result );
extern struct elliptic_curve x25519_curve;
#endif /* _IPXE_X25519_H */ #endif /* _IPXE_X25519_H */