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-rw-r--r--src/crypto/sha256-prf.c38
1 files changed, 36 insertions, 2 deletions
diff --git a/src/crypto/sha256-prf.c b/src/crypto/sha256-prf.c
index 0da6d13..9a11208 100644
--- a/src/crypto/sha256-prf.c
+++ b/src/crypto/sha256-prf.c
@@ -1,6 +1,6 @@
/*
* SHA256-based PRF (IEEE 802.11r)
- * Copyright (c) 2003-2007, Jouni Malinen <j@w1.fi>
+ * Copyright (c) 2003-2013, Jouni Malinen <j@w1.fi>
*
* This software may be distributed under the terms of the BSD license.
* See README for more details.
@@ -29,12 +29,36 @@
void sha256_prf(const u8 *key, size_t key_len, const char *label,
const u8 *data, size_t data_len, u8 *buf, size_t buf_len)
{
+ sha256_prf_bits(key, key_len, label, data, data_len, buf, buf_len * 8);
+}
+
+
+/**
+ * sha256_prf_bits - IEEE Std 802.11-2012, 11.6.1.7.2 Key derivation function
+ * @key: Key for KDF
+ * @key_len: Length of the key in bytes
+ * @label: A unique label for each purpose of the PRF
+ * @data: Extra data to bind into the key
+ * @data_len: Length of the data
+ * @buf: Buffer for the generated pseudo-random key
+ * @buf_len: Number of bits of key to generate
+ *
+ * This function is used to derive new, cryptographically separate keys from a
+ * given key. If the requested buf_len is not divisible by eight, the least
+ * significant 1-7 bits of the last octet in the output are not part of the
+ * requested output.
+ */
+void sha256_prf_bits(const u8 *key, size_t key_len, const char *label,
+ const u8 *data, size_t data_len, u8 *buf,
+ size_t buf_len_bits)
+{
u16 counter = 1;
size_t pos, plen;
u8 hash[SHA256_MAC_LEN];
const u8 *addr[4];
size_t len[4];
u8 counter_le[2], length_le[2];
+ size_t buf_len = (buf_len_bits + 7) / 8;
addr[0] = counter_le;
len[0] = 2;
@@ -45,7 +69,7 @@ void sha256_prf(const u8 *key, size_t key_len, const char *label,
addr[3] = length_le;
len[3] = sizeof(length_le);
- WPA_PUT_LE16(length_le, buf_len * 8);
+ WPA_PUT_LE16(length_le, buf_len_bits);
pos = 0;
while (pos < buf_len) {
plen = buf_len - pos;
@@ -57,8 +81,18 @@ void sha256_prf(const u8 *key, size_t key_len, const char *label,
} else {
hmac_sha256_vector(key, key_len, 4, addr, len, hash);
os_memcpy(&buf[pos], hash, plen);
+ pos += plen;
break;
}
counter++;
}
+
+ /*
+ * Mask out unused bits in the last octet if it does not use all the
+ * bits.
+ */
+ if (buf_len_bits % 8) {
+ u8 mask = 0xff << (8 - buf_len_bits % 8);
+ buf[pos - 1] &= mask;
+ }
}