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/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/*
ARCFOUR cipher (based on a cipher posted on the Usenet in Spring-95).
This cipher is widely believed and has been tested to be equivalent
with the RC4 cipher from RSA Data Security, Inc. (RC4 is a trademark
of RSA Data Security)
*/
#include "k5-int.h"
#include "arcfour-int.h"
#include "hash_provider/hash_provider.h"
const char l40[] = "fortybits";
void
krb5int_arcfour_encrypt_length(const struct krb5_enc_provider *enc,
const struct krb5_hash_provider *hash,
size_t inputlen, size_t *length)
{
/* checksum + (confounder + inputlen, in even blocksize) */
*length = hash->hashsize + krb5_roundup(8 + inputlen, enc->block_size);
}
krb5_keyusage
krb5int_arcfour_translate_usage(krb5_keyusage usage)
{
switch (usage) {
case 1: return 1; /* AS-REQ PA-ENC-TIMESTAMP padata timestamp, */
case 2: return 2; /* ticket from kdc */
case 3: return 8; /* as-rep encrypted part */
case 4: return 4; /* tgs-req authz data */
case 5: return 5; /* tgs-req authz data in subkey */
case 6: return 6; /* tgs-req authenticator cksum */
case 7: return 7; /* tgs-req authenticator */
case 8: return 8;
case 9: return 9; /* tgs-rep encrypted with subkey */
case 10: return 10; /* ap-rep authentication cksum (never used by MS) */
case 11: return 11; /* app-req authenticator */
case 12: return 12; /* app-rep encrypted part */
case 23: return 13; /* sign wrap token*/
default: return usage;
}
}
/* Derive a usage key from a session key and krb5 usage constant. */
krb5_error_code
krb5int_arcfour_usage_key(const struct krb5_enc_provider *enc,
const struct krb5_hash_provider *hash,
const krb5_keyblock *session_keyblock,
krb5_keyusage usage,
krb5_keyblock *out)
{
char salt_buf[14];
krb5_data out_data = make_data(out->contents, out->length);
krb5_data salt = make_data(salt_buf, sizeof(salt_buf));
krb5_keyusage ms_usage;
/* Generate the salt. */
ms_usage = krb5int_arcfour_translate_usage(usage);
if (session_keyblock->enctype == ENCTYPE_ARCFOUR_HMAC_EXP) {
memcpy(salt_buf, l40, 10);
store_32_le(ms_usage, salt_buf + 10);
} else {
salt.length=4;
store_32_le(ms_usage, salt_buf);
}
/* Compute HMAC(key, salt) to produce the usage key. */
return krb5int_hmac_keyblock(hash, session_keyblock, 1, &salt, &out_data);
}
/* Derive an encryption key from a usage key and (typically) checksum. */
krb5_error_code
krb5int_arcfour_enc_key(const struct krb5_enc_provider *enc,
const struct krb5_hash_provider *hash,
const krb5_keyblock *usage_keyblock,
const krb5_data *checksum, krb5_keyblock *out)
{
krb5_keyblock *trunc_keyblock = NULL;
krb5_data out_data = make_data(out->contents, out->length);
krb5_error_code ret;
/* Copy usage_keyblock to trunc_keyblock and truncate if exportable. */
ret = krb5int_c_copy_keyblock(NULL, usage_keyblock, &trunc_keyblock);
if (ret != 0)
return ret;
if (trunc_keyblock->enctype == ENCTYPE_ARCFOUR_HMAC_EXP)
memset(trunc_keyblock->contents + 7, 0xab, 9);
/* Compute HMAC(trunc_key, checksum) to produce the encryption key. */
ret = krb5int_hmac_keyblock(hash, trunc_keyblock, 1, checksum, &out_data);
krb5int_c_free_keyblock(NULL, trunc_keyblock);
return ret;
}
krb5_error_code
krb5int_arcfour_encrypt(const struct krb5_enc_provider *enc,
const struct krb5_hash_provider *hash,
krb5_key key, krb5_keyusage usage,
const krb5_data *ivec, const krb5_data *input,
krb5_data *output)
{
krb5_keyblock *usage_keyblock = NULL, *enc_keyblock = NULL;
krb5_key enc_key;
krb5_data plaintext = empty_data();
krb5_data checksum, ciphertext, confounder;
krb5_error_code ret;
unsigned int plainlen;
/* Allocate buffers. */
plainlen = krb5_roundup(input->length + CONFOUNDERLENGTH, enc->block_size);
ret = alloc_data(&plaintext, plainlen);
if (ret != 0)
goto cleanup;
ret = krb5int_c_init_keyblock(NULL, key->keyblock.enctype, enc->keybytes,
&usage_keyblock);
if (ret != 0)
goto cleanup;
ret = krb5int_c_init_keyblock(NULL, key->keyblock.enctype, enc->keybytes,
&enc_keyblock);
if (ret != 0)
goto cleanup;
/* Set up subsets of output and plaintext. */
checksum = make_data(output->data, hash->hashsize);
ciphertext = make_data(output->data + hash->hashsize, plainlen);
confounder = make_data(plaintext.data, CONFOUNDERLENGTH);
/* Derive a usage key from the session key and usage. */
ret = krb5int_arcfour_usage_key(enc, hash, &key->keyblock, usage,
usage_keyblock);
if (ret != 0)
goto cleanup;
/* Compose a confounder with the input data to form the plaintext. */
ret = krb5_c_random_make_octets(NULL, &confounder);
memcpy(plaintext.data + confounder.length, input->data, input->length);
if (ret)
goto cleanup;
/* Compute HMAC(usage key, plaintext) to get the checksum. */
ret = krb5int_hmac_keyblock(hash, usage_keyblock, 1, &plaintext,
&checksum);
if (ret)
goto cleanup;
/* Derive the encryption key from the usage key and checksum. */
ret = krb5int_arcfour_enc_key(enc, hash, usage_keyblock, &checksum,
enc_keyblock);
if (ret)
goto cleanup;
/* Encrypt the plaintext. */
ret = krb5_k_create_key(NULL, enc_keyblock, &enc_key);
if (ret)
goto cleanup;
ret = (*enc->encrypt)(enc_key, ivec, &plaintext, &ciphertext);
krb5_k_free_key(NULL, enc_key);
if (ret)
goto cleanup;
output->length = plainlen + hash->hashsize;
cleanup:
krb5int_c_free_keyblock(NULL, usage_keyblock);
krb5int_c_free_keyblock(NULL, enc_keyblock);
zapfree(plaintext.data, plaintext.length);
return ret;
}
krb5_error_code
krb5int_arcfour_decrypt(const struct krb5_enc_provider *enc,
const struct krb5_hash_provider *hash,
krb5_key key, krb5_keyusage usage,
const krb5_data *ivec, const krb5_data *input,
krb5_data *output)
{
krb5_keyblock *usage_keyblock = NULL, *enc_keyblock = NULL;
krb5_data plaintext = empty_data(), comp_checksum = empty_data();
krb5_data checksum, ciphertext;
krb5_key enc_key;
krb5_error_code ret;
/* Set up subsets of input. */
checksum = make_data(input->data, hash->hashsize);
ciphertext = make_data(input->data + hash->hashsize,
input->length - hash->hashsize);
/* Allocate buffers. */
ret = alloc_data(&plaintext, ciphertext.length);
if (ret != 0)
goto cleanup;
ret = alloc_data(&comp_checksum, hash->hashsize);
if (ret != 0)
goto cleanup;
ret = krb5int_c_init_keyblock(NULL, key->keyblock.enctype, enc->keybytes,
&usage_keyblock);
if (ret != 0)
goto cleanup;
ret = krb5int_c_init_keyblock(NULL, key->keyblock.enctype, enc->keybytes,
&enc_keyblock);
if (ret != 0)
goto cleanup;
/* We may have to try two usage values; see below. */
do {
/* Derive a usage key from the session key and usage. */
ret = krb5int_arcfour_usage_key(enc, hash, &key->keyblock, usage,
usage_keyblock);
if (ret != 0)
goto cleanup;
/* Derive the encryption key from the usage key and checksum. */
ret = krb5int_arcfour_enc_key(enc, hash, usage_keyblock, &checksum,
enc_keyblock);
if (ret)
goto cleanup;
/* Decrypt the ciphertext. */
ret = krb5_k_create_key(NULL, enc_keyblock, &enc_key);
if (ret)
goto cleanup;
ret = (*enc->decrypt)(enc_key, ivec, &ciphertext, &plaintext);
krb5_k_free_key(NULL, enc_key);
if (ret)
goto cleanup;
/* Compute HMAC(usage key, plaintext) to get the checksum. */
ret = krb5int_hmac_keyblock(hash, usage_keyblock, 1, &plaintext,
&comp_checksum);
if (ret)
goto cleanup;
if (memcmp(checksum.data, comp_checksum.data, hash->hashsize) != 0) {
if (usage == 9) {
/*
* RFC 4757 specifies usage 8 for TGS-REP encrypted
* parts encrypted in a subkey, but the value used by MS
* is actually 9. We now use 9 to start with, but fall
* back to 8 on failure in case we are communicating
* with a KDC using the value from the RFC.
*/
usage = 8;
continue;
}
ret = KRB5KRB_AP_ERR_BAD_INTEGRITY;
goto cleanup;
}
break;
} while (1);
/* Remove the confounder from the plaintext to get the output. */
memcpy(output->data, plaintext.data + CONFOUNDERLENGTH,
plaintext.length - CONFOUNDERLENGTH);
output->length = plaintext.length - CONFOUNDERLENGTH;
cleanup:
krb5int_c_free_keyblock(NULL, usage_keyblock);
krb5int_c_free_keyblock(NULL, enc_keyblock);
zapfree(plaintext.data, plaintext.length);
zapfree(comp_checksum.data, comp_checksum.length);
return ret;
}
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