add a helper function

d0_blind_id_authenticate_with_private_id_generate_missing_signature to generate
NON-blind signatures:

Server shall:
- load private key

Both shall:
- perform authentication as usual

Server shall:
- notice that the status is false
- call d0_blind_id_authenticate_with_private_id_generate_missing_signature
- write public ID
- send that data to client

Client shall:
- read own private ID
- get fingerprint
- read received public ID (leaves the private part alone)
- verify fingerprint
- possibly verify ID
- write own private ID again

diff --git a/Makefile.am b/Makefile.am
index 89a0886e0bd276738a129c60f56df9b91d3df160..31a92beef5ccdff8afbf58a4a73b37128d12f4a0 100644 (file)
--- a/Makefile.am
+++ b/Makefile.am
@@ -12,7 +12,7 @@ lib_LTLIBRARIES = libd0_blind_id.la
 
 libd0_blind_id_la_SOURCES = d0_bignum-gmp.c d0_blind_id.c d0.c d0_iobuf.c sha2.c \
                             d0_bignum-gmp.h d0_blind_id.h d0.h d0_iobuf.h sha2.h
-libd0_blind_id_la_LDFLAGS = -versioninfo 2:0:2
+libd0_blind_id_la_LDFLAGS = -versioninfo 3:0:3
 libd0_blind_id_la_CFLAGS = -fvisibility=hidden -Wold-style-definition -Wstrict-prototypes -Wsign-compare -Wdeclaration-after-statement
 library_includedir = $(includedir)/d0_blind_id
 library_include_HEADERS = d0_blind_id.h d0.h

diff --git a/d0_blind_id.c b/d0_blind_id.c
index cc85624e5cc8e680f8251dc09da0366135e81496..4989e9e33cef7f32f22253a4be883acc19f3a8a7 100644 (file)
--- a/d0_blind_id.c
+++ b/d0_blind_id.c
@@ -979,6 +979,31 @@ fail:
        return 0;
 }
 
+WARN_UNUSED_RESULT BOOL d0_blind_id_authenticate_with_private_id_generate_missing_signature(d0_blind_id_t *ctx)
+{
+       size_t sz;
+       static unsigned char shabuf[2048];
+
+       REPLACING(schnorr_H_g_to_s_signature);
+       USING(schnorr_g_to_s); USING(rsa_d); USING(rsa_n);
+
+       // we will actually sign SHA(4^s) to prevent a malleability attack!
+       CHECK(d0_bignum_mov(temp2, ctx->schnorr_g_to_s));
+       sz = (d0_bignum_size(ctx->rsa_n) + 7) / 8; // this is too long, so we have to take the value % rsa_n when "decrypting"
+       if(sz > sizeof(shabuf))
+               sz = sizeof(shabuf);
+       CHECK(d0_longhash_destructive(temp2, shabuf, sz));
+       CHECK(d0_bignum_import_unsigned(temp2, shabuf, sz));
+
+       // + 7 / 8 is too large, so let's mod it
+       CHECK(d0_bignum_divmod(NULL, temp1, temp2, ctx->rsa_n));
+       CHECK(d0_bignum_mod_pow(ctx->schnorr_H_g_to_s_signature, temp1, ctx->rsa_d, ctx->rsa_n));
+       return 1;
+
+fail:
+       return 0;
+}
+
 WARN_UNUSED_RESULT BOOL d0_blind_id_fingerprint64_public_id(const d0_blind_id_t *ctx, char *outbuf, size_t *outbuflen)
 {
        d0_iobuf_t *out = NULL;

diff --git a/d0_blind_id.h b/d0_blind_id.h
index cc5afba4b99fa957150867db9fa6dc0309478707..15768a6742ebd715045083d8c96c65c6ded173cd 100644 (file)
--- a/d0_blind_id.h
+++ b/d0_blind_id.h
@@ -34,6 +34,7 @@ EXPORT WARN_UNUSED_RESULT BOOL d0_blind_id_authenticate_with_private_id_start(d0
 EXPORT WARN_UNUSED_RESULT BOOL d0_blind_id_authenticate_with_private_id_challenge(d0_blind_id_t *ctx, BOOL is_first, BOOL recv_modulus, const char *inbuf, size_t inbuflen, char *outbuf, size_t *outbuflen, BOOL *status);
 EXPORT WARN_UNUSED_RESULT BOOL d0_blind_id_authenticate_with_private_id_response(d0_blind_id_t *ctx, const char *inbuf, size_t inbuflen, char *outbuf, size_t *outbuflen);
 EXPORT WARN_UNUSED_RESULT BOOL d0_blind_id_authenticate_with_private_id_verify(d0_blind_id_t *ctx, const char *inbuf, size_t inbuflen, char *msg, size_t *msglen, BOOL *status);
+EXPORT WARN_UNUSED_RESULT BOOL d0_blind_id_authenticate_with_private_id_generate_missing_signature(d0_blind_id_t *ctx);
 EXPORT WARN_UNUSED_RESULT BOOL d0_blind_id_fingerprint64_public_id(const d0_blind_id_t *ctx, char *outbuf, size_t *outbuflen);
 EXPORT WARN_UNUSED_RESULT BOOL d0_blind_id_sessionkey_public_id(const d0_blind_id_t *ctx, char *outbuf, size_t *outbuflen); // can only be done after successful key exchange, this performs a modpow; key length is limited by SHA_DIGESTSIZE for now; also ONLY valid after successful d0_blind_id_authenticate_with_private_id_verify/d0_blind_id_fingerprint64_public_id