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| -rw-r--r-- | yarrow_key_event.c | 72 |
1 files changed, 72 insertions, 0 deletions
diff --git a/yarrow_key_event.c b/yarrow_key_event.c new file mode 100644 index 00000000..9ddbb00b --- /dev/null +++ b/yarrow_key_event.c @@ -0,0 +1,72 @@ +/* yarrow_key_event.c + * + * Exampel entropy estimator for key-like input events. */ + +/* nettle, low-level cryptographics library + * + * Copyright (C) 2001 Niels Möller + * + * The nettle library is free software; you can redistribute it and/or modify + * it under the terms of the GNU Lesser General Public License as published by + * the Free Software Foundation; either version 2.1 of the License, or (at your + * option) any later version. + * + * The nettle library is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY + * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public + * License for more details. + * + * You should have received a copy of the GNU Lesser General Public License + * along with the nettle library; see the file COPYING.LIB. If not, write to + * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, + * MA 02111-1307, USA. + */ + +#include "yarrow.h" + +void +yarrow_key_event_init(struct yarrow_key_event_ctx *ctx) +{ + unsigned i; + + ctx->index = 0; + for (i = 0; i < YARROW_KEY_EVENT_BUFFER; i++) + ctx->chars[i] = 0; +} + +unsigned +yarrow_key_event_estimate(struct yarrow_key_event_ctx *ctx, + unsigned key, unsigned time) +{ + unsigned entropy = 0; + unsigned i; + + /* Look at timing first. */ + if (ctx->index) + { + if ( (time - ctx->previous) < 256) + entropy++; + } + ctx->previous = time; + + if (!key) + return entropy; + + for (i = 0; i < YARROW_KEY_EVENT_BUFFER; i++) + if (key == ctx->chars[i]) + /* This is a recent character. Ignore it. */ + return entropy; + + /* Count one bit of entropy, unless this was one of the initial 16 + * characters. */ + if (ctx->chars[ctx->index]) + entropy++; + + /* Remember the character. */ + + ctx->chars[ctx->index] = key; + ctx->index = (ctx->index + 1) % YARROW_KEY_EVENT_BUFFER; + + return entropy; +} + |