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Implement Diffie-Hellman computations in crypto backends. (#149)

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Not all backends feature the low level API needed to compute a Diffie-Hellman
secret, but some of them directly implement Diffie-Hellman support with opaque
private data. The later approach is now generalized and backends are
responsible for all Diffie Hellman computations.
As a side effect, procedures/macros _libssh2_bn_rand and _libssh2_bn_mod_exp
are no longer needed outside the backends.
This commit is contained in:
monnerat
2016-11-27 19:39:00 +01:00
committed by Alexander Lamaison
parent 5abceec571
commit f7daf3185a
10 changed files with 215 additions and 96 deletions
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24
docs/HACKING.CRYPTO
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@@ -338,13 +338,6 @@ TripleDES-CBC algorithm identifier initializer.
5) Diffie-Hellman support.
If the crypto-library supports opaque Diffie-Hellman computations, symbol
`libssh2_dh_key_pair' should be #defined as described below and the rest of
this section applies.
Else, the Diffie-Hellman context MUST be defined as `_libssh2_bn *' and
the computation is emulated via calls to _libssh2_bn_rand() and
_libssh2_bn_mod_exp(): all other symbols in this section are unused in this
case.
5.1) Diffie-Hellman context.
_libssh2_dh_ctx
@@ -364,7 +357,6 @@ Generates a Diffie-Hellman key pair using base `g', prime `p' and the given
The private key is stored as opaque in the Diffie-Hellman context `*dhctx' and
the public key is returned in `public'.
0 is returned upon success, else -1.
If defined, this procedure MUST be implemented as a #define'd macro.
int libssh2_dh_secret(_libssh2_dh_ctx *dhctx, _libssh2_bn *secret,
_libssh2_bn *f, _libssh2_bn *p, _libssh2_bn_ctx * bnctx)
@@ -434,22 +426,6 @@ Converts the absolute value of bn into big-endian form and store it at
val. val must point to _libssh2_bn_bytes(bn) bytes of memory.
Returns the length of the big-endian number.
void _libssh2_bn_rand(_libssh2_bn *bn, int bits, int top, int bottom);
Generates a cryptographically strong pseudo-random number of bits in
length and stores it in bn. If top is -1, the most significant bit of the
random number can be zero. If top is 0, it is set to 1, and if top is 1, the
two most significant bits of the number will be set to 1, so that the product
of two such random numbers will always have 2*bits length. If bottom is true,
the number will be odd.
This procedure is only needed if no specific Diffie-Hellman support is provided.
void _libssh2_bn_mod_exp(_libssh2_bn *r, _libssh2_bn *a,
_libssh2_bn *p, _libssh2_bn *m,
_libssh2_bn_ctx *ctx);
Computes a to the p-th power modulo m and stores the result into r (r=a^p % m).
May use the given context.
This procedure is only needed if no specific Diffie-Hellman support is provided.
7) Private key algorithms.
Format of an RSA public key: