commit 559658ff1ca1492543ad60d10b7101c70a62eaa2 Author: George Kadianakis desnacked@riseup.net Date: Tue Apr 25 15:19:41 2017 +0300

ed25519: Add func that checks for torsion component in pubkeys.

See https://lists.torproject.org/pipermail/tor-dev/2017-April/012213.html . --- changes/bug22006 | 4 +++ src/common/crypto_ed25519.c | 50 +++++++++++++++++++++++++++++++ src/common/crypto_ed25519.h | 2 ++ src/ext/ed25519/donna/ed25519_donna_tor.h | 5 ++++ src/ext/ed25519/donna/ed25519_tor.c | 27 +++++++++++++++++ src/ext/ed25519/ref10/blinding.c | 37 +++++++++++++++++++++++ src/ext/ed25519/ref10/ed25519_ref10.h | 4 +++ 7 files changed, 129 insertions(+)

diff --git a/changes/bug22006 b/changes/bug22006 new file mode 100644 index 0000000..912bdd8 --- /dev/null +++ b/changes/bug22006 @@ -0,0 +1,4 @@ + o Minor features (ed25519): + - Add validation function that checks for torsion components in ed25119 + public keys. Currently unused but will be used by prop224 client-side + code. Addresses ticket #22006. Math help by Ian Goldberg. diff --git a/src/common/crypto_ed25519.c b/src/common/crypto_ed25519.c index 188e18c..6ebb2a7 100644 --- a/src/common/crypto_ed25519.c +++ b/src/common/crypto_ed25519.c @@ -28,6 +28,7 @@ #include "crypto_format.h" #include "torlog.h" #include "util.h" +#include "util_format.h"

#include "ed25519/ref10/ed25519_ref10.h" #include "ed25519/donna/ed25519_donna_tor.h" @@ -57,6 +58,9 @@ typedef struct {

int (*pubkey_from_curve25519_pubkey)(unsigned char *, const unsigned char *, int); + + int (*ed25519_scalarmult_with_group_order)(unsigned char *, + const unsigned char *); } ed25519_impl_t;

/** The Ref10 Ed25519 implementation. This one is pure C and lightly @@ -77,6 +81,7 @@ static const ed25519_impl_t impl_ref10 = { ed25519_ref10_blind_public_key,

ed25519_ref10_pubkey_from_curve25519_pubkey, + ed25519_ref10_scalarmult_with_group_order, };

/** The Ref10 Ed25519 implementation. This one is heavily optimized, but still @@ -97,6 +102,7 @@ static const ed25519_impl_t impl_donna = { ed25519_donna_blind_public_key,

ed25519_donna_pubkey_from_curve25519_pubkey, + ed25519_donna_scalarmult_with_group_order, };

/** Which Ed25519 implementation are we using? NULL if we haven't decided @@ -754,3 +760,47 @@ ed25519_init(void) pick_ed25519_impl(); }

+/* Return true if <b>point</b> is the identity element of the ed25519 group. */ +static int +ed25519_point_is_identity_element(const uint8_t *point) +{ + /* The identity element in ed25159 is the point with coordinates (0,1). */ + static const uint8_t ed25519_identity[32] = { + 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }; + tor_assert(sizeof(ed25519_identity) == ED25519_PUBKEY_LEN); + return tor_memeq(point, ed25519_identity, sizeof(ed25519_identity)); +} + +/** Validate <b>pubkey</b> to ensure that it has no torsion component. + * Return 0 if <b>pubkey</b> is valid, else return -1. */ +int +ed25519_validate_pubkey(const ed25519_public_key_t *pubkey) +{ + uint8_t result[32] = {9}; + + /* First check that we were not given the identity element */ + if (ed25519_point_is_identity_element(pubkey->pubkey)) { + log_warn(LD_CRYPTO, "ed25519 pubkey is the identity\n"); + return -1; + } + + /* For any point on the curve, doing l*point should give the identity element + * (where l is the group order). Do the computation and check that the + * identity element is returned. */ + if (get_ed_impl()->ed25519_scalarmult_with_group_order(result, + pubkey->pubkey) < 0) { + log_warn(LD_CRYPTO, "ed25519 group order scalarmult failed\n"); + return -1; + } + + if (!ed25519_point_is_identity_element(result)) { + log_warn(LD_CRYPTO, "ed25519 validation failed\n"); + return -1; + } + + return 0; +} + diff --git a/src/common/crypto_ed25519.h b/src/common/crypto_ed25519.h index 77a3313..3a43920 100644 --- a/src/common/crypto_ed25519.h +++ b/src/common/crypto_ed25519.h @@ -127,6 +127,8 @@ void ed25519_pubkey_copy(ed25519_public_key_t *dest, void ed25519_set_impl_params(int use_donna); void ed25519_init(void);

+int ed25519_validate_pubkey(const ed25519_public_key_t *pubkey); + #ifdef TOR_UNIT_TESTS void crypto_ed25519_testing_force_impl(const char *name); void crypto_ed25519_testing_restore_impl(void); diff --git a/src/ext/ed25519/donna/ed25519_donna_tor.h b/src/ext/ed25519/donna/ed25519_donna_tor.h index d225407..7d7b8c0 100644 --- a/src/ext/ed25519/donna/ed25519_donna_tor.h +++ b/src/ext/ed25519/donna/ed25519_donna_tor.h @@ -30,4 +30,9 @@ int ed25519_donna_blind_public_key(unsigned char *out, const unsigned char *inp, int ed25519_donna_pubkey_from_curve25519_pubkey(unsigned char *out, const unsigned char *inp, int signbit);

+ +int +ed25519_donna_scalarmult_with_group_order(unsigned char *out, + const unsigned char *pubkey); + #endif diff --git a/src/ext/ed25519/donna/ed25519_tor.c b/src/ext/ed25519/donna/ed25519_tor.c index 9537ae6..bd11027 100644 --- a/src/ext/ed25519/donna/ed25519_tor.c +++ b/src/ext/ed25519/donna/ed25519_tor.c @@ -340,5 +340,32 @@ ed25519_donna_pubkey_from_curve25519_pubkey(unsigned char *out, return 0; }

+/* Do the scalar multiplication of <b>pubkey</b> with the group order + * <b>modm_m</b>. Place the result in <b>out</b> which must be at least 32 + * bytes long. */ +int +ed25519_donna_scalarmult_with_group_order(unsigned char *out, + const unsigned char *pubkey) +{ + static const bignum256modm ALIGN(16) zero = { 0 }; + unsigned char pkcopy[32]; + ge25519 ALIGN(16) Point, Result; + + /* No "ge25519_unpack", negate the public key and unpack it back. + * See ed25519_donna_blind_public_key() */ + memcpy(pkcopy, pubkey, 32); + pkcopy[31] ^= (1<<7); + if (!ge25519_unpack_negative_vartime(&Point, pkcopy)) { + return -1; /* error: bail out */ + } + + /* There is no regular scalarmult function so we have to do: + * Result = l*P + 0*B */ + ge25519_double_scalarmult_vartime(&Result, &Point, modm_m, zero); + ge25519_pack(out, &Result); + + return 0; +} + #include "test-internals.c"

diff --git a/src/ext/ed25519/ref10/blinding.c b/src/ext/ed25519/ref10/blinding.c index ee3e866..8503f90 100644 --- a/src/ext/ed25519/ref10/blinding.c +++ b/src/ext/ed25519/ref10/blinding.c @@ -74,3 +74,40 @@ int ed25519_ref10_blind_public_key(unsigned char *out,

return 0; } + +/* This is the group order encoded in a format that + * ge_double_scalarmult_vartime() understands. The group order m is: + * m = 2^252 + 27742317777372353535851937790883648493 = + * 0x1000000000000000000000000000000014def9dea2f79cd65812631a5cf5d3ed + */ +static const uint8_t modm_m[32] = {0xed,0xd3,0xf5,0x5c,0x1a,0x63,0x12,0x58, + 0xd6,0x9c,0xf7,0xa2,0xde,0xf9,0xde,0x14, + 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, + 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x10}; + +/* Do the scalar multiplication of <b>pubkey</b> with the group order + * <b>modm_m</b>. Place the result in <b>out</b> which must be at least 32 + * bytes long. */ +int +ed25519_ref10_scalarmult_with_group_order(unsigned char *out, + const unsigned char *pubkey) +{ + unsigned char pkcopy[32]; + unsigned char zero[32] = {0}; + ge_p3 Point; + ge_p2 Result; + + /* All this is done to fit 'pubkey' in 'Point' so that it can be used by + * ed25519 ref code. Same thing as in blinding function */ + memcpy(pkcopy, pubkey, 32); + pkcopy[31] ^= (1<<7); + if (ge_frombytes_negate_vartime(&Point, pkcopy) != 0) { + return -1; /* error: bail out */ + } + + /* There isn't a regular scalarmult -- we have to do r = l*P + 0*B */ + ge_double_scalarmult_vartime(&Result, modm_m, &Point, zero); + ge_tobytes(out, &Result); + + return 0; +} diff --git a/src/ext/ed25519/ref10/ed25519_ref10.h b/src/ext/ed25519/ref10/ed25519_ref10.h index af7e21a..5965694 100644 --- a/src/ext/ed25519/ref10/ed25519_ref10.h +++ b/src/ext/ed25519/ref10/ed25519_ref10.h @@ -27,4 +27,8 @@ int ed25519_ref10_blind_public_key(unsigned char *out, const unsigned char *inp, const unsigned char *param);

+int +ed25519_ref10_scalarmult_with_group_order(unsigned char *out, + const unsigned char *pubkey); + #endif