[digest] Add HMAC-SHA1 based pseudorandom function and PBKDF2

Both of these routines are used by 802.11 WPA, but they are generic and could be needed by other protocols as well. Signed-off-by: Marty Connor <mdc@etherboot.org>
ipxe · Jan 5, 2010 · 59b7d00 · 59b7d00
1 parent 05d3be1
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diff --git a/src/crypto/sha1extra.c b/src/crypto/sha1extra.c
@@ -0,0 +1,165 @@
+/*
+ * Copyright (c) 2009 Joshua Oreman <oremanj@rwcr.net>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program 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
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <gpxe/crypto.h>
+#include <gpxe/sha1.h>
+#include <gpxe/hmac.h>
+#include <stdint.h>
+#include <byteswap.h>
+
+/**
+ * SHA1 pseudorandom function for creating derived keys
+ *
+ * @v key	Master key with which this call is associated
+ * @v key_len	Length of key
+ * @v label	NUL-terminated ASCII string describing purpose of PRF data
+ * @v data	Further data that should be included in the PRF
+ * @v data_len	Length of further PRF data
+ * @v prf_len	Bytes of PRF to generate
+ * @ret prf	Pseudorandom function bytes
+ *
+ * This is the PRF variant used by 802.11, defined in IEEE 802.11-2007
+ * 8.5.5.1. EAP-FAST uses a different SHA1-based PRF, and TLS uses an
+ * MD5-based PRF.
+ */
+void prf_sha1 ( const void *key, size_t key_len, const char *label,
+		const void *data, size_t data_len, void *prf, size_t prf_len )
+{
+	u32 blk;
+	u8 keym[key_len];	/* modifiable copy of key */
+	u8 in[strlen ( label ) + 1 + data_len + 1]; /* message to HMAC */
+	u8 *in_blknr;		/* pointer to last byte of in, block number */
+	u8 out[SHA1_SIZE];	/* HMAC-SHA1 result */
+	u8 sha1_ctx[SHA1_CTX_SIZE]; /* SHA1 context */
+	const size_t label_len = strlen ( label );
+
+	/* The HMAC-SHA-1 is calculated using the given key on the
+	   message text `label', followed by a NUL, followed by one
+	   byte indicating the block number (0 for first). */
+
+	memcpy ( keym, key, key_len );
+
+	memcpy ( in, label, strlen ( label ) + 1 );
+	memcpy ( in + label_len + 1, data, data_len );
+	in_blknr = in + label_len + 1 + data_len;
+
+	for ( blk = 0 ;; blk++ ) {
+		*in_blknr = blk;
+
+		hmac_init ( &sha1_algorithm, sha1_ctx, keym, &key_len );
+		hmac_update ( &sha1_algorithm, sha1_ctx, in, sizeof ( in ) );
+		hmac_final ( &sha1_algorithm, sha1_ctx, keym, &key_len, out );
+
+		if ( prf_len <= SHA1_SIZE ) {
+			memcpy ( prf, out, prf_len );
+			break;
+		}
+
+		memcpy ( prf, out, SHA1_SIZE );
+		prf_len -= SHA1_SIZE;
+		prf += SHA1_SIZE;
+	}
+}
+
+/**
+ * PBKDF2 key derivation function inner block operation
+ *
+ * @v passphrase	Passphrase from which to derive key
+ * @v pass_len		Length of passphrase
+ * @v salt		Salt to include in key
+ * @v salt_len		Length of salt
+ * @v iterations	Number of iterations of SHA1 to perform
+ * @v blocknr		Index of this block, starting at 1
+ * @ret block		SHA1_SIZE bytes of PBKDF2 data
+ *
+ * The operation of this function is described in RFC 2898.
+ */
+static void pbkdf2_sha1_f ( const void *passphrase, size_t pass_len,
+			    const void *salt, size_t salt_len,
+			    int iterations, u32 blocknr, u8 *block )
+{
+	u8 pass[pass_len];	/* modifiable passphrase */
+	u8 in[salt_len + 4];	/* input buffer to first round */
+	u8 last[SHA1_SIZE];	/* output of round N, input of N+1 */
+	u8 sha1_ctx[SHA1_CTX_SIZE];
+	u8 *next_in = in;	/* changed to `last' after first round */
+	int next_size = sizeof ( in );
+	int i, j;
+
+	blocknr = htonl ( blocknr );
+
+	memcpy ( pass, passphrase, pass_len );
+	memcpy ( in, salt, salt_len );
+	memcpy ( in + salt_len, &blocknr, 4 );
+	memset ( block, 0, SHA1_SIZE );
+
+	for ( i = 0; i < iterations; i++ ) {
+		hmac_init ( &sha1_algorithm, sha1_ctx, pass, &pass_len );
+		hmac_update ( &sha1_algorithm, sha1_ctx, next_in, next_size );
+		hmac_final ( &sha1_algorithm, sha1_ctx, pass, &pass_len, last );
+
+		for ( j = 0; j < SHA1_SIZE; j++ ) {
+			block[j] ^= last[j];
+		}
+
+		next_in = last;
+		next_size = SHA1_SIZE;
+	}
+}
+
+/**
+ * PBKDF2 key derivation function using SHA1
+ *
+ * @v passphrase	Passphrase from which to derive key
+ * @v pass_len		Length of passphrase
+ * @v salt		Salt to include in key
+ * @v salt_len		Length of salt
+ * @v iterations	Number of iterations of SHA1 to perform
+ * @v key_len		Length of key to generate
+ * @ret key		Generated key bytes
+ *
+ * This is used most notably in 802.11 WPA passphrase hashing, in
+ * which case the salt is the SSID, 4096 iterations are used, and a
+ * 32-byte key is generated that serves as the Pairwise Master Key for
+ * EAPOL authentication.
+ *
+ * The operation of this function is further described in RFC 2898.
+ */
+void pbkdf2_sha1 ( const void *passphrase, size_t pass_len,
+		   const void *salt, size_t salt_len,
+		   int iterations, void *key, size_t key_len )
+{
+	u32 blocks = ( key_len + SHA1_SIZE - 1 ) / SHA1_SIZE;
+	u32 blk;
+	u8 buf[SHA1_SIZE];
+
+	for ( blk = 1; blk <= blocks; blk++ ) {
+		pbkdf2_sha1_f ( passphrase, pass_len, salt, salt_len,
+				iterations, blk, buf );
+		if ( key_len <= SHA1_SIZE ) {
+			memcpy ( key, buf, key_len );
+			break;
+		}
+
+		memcpy ( key, buf, SHA1_SIZE );
+		key_len -= SHA1_SIZE;
+		key += SHA1_SIZE;
+	}
+}
diff --git a/src/include/gpxe/sha1.h b/src/include/gpxe/sha1.h
@@ -12,4 +12,13 @@ struct digest_algorithm;
 
 extern struct digest_algorithm sha1_algorithm;
 
+/* SHA1-wrapping functions defined in sha1extra.c: */
+
+void prf_sha1 ( const void *key, size_t key_len, const char *label,
+		const void *data, size_t data_len, void *prf, size_t prf_len );
+
+void pbkdf2_sha1 ( const void *passphrase, size_t pass_len,
+		   const void *salt, size_t salt_len,
+		   int iterations, void *key, size_t key_len );
+
 #endif /* _GPXE_SHA1_H */