+/*
+ * Note that RC4 depends on deriving keys using the sequence
+ * number or the checksum of a token. Therefore, the final keys
+ * cannot be calculated until the token is being constructed!
+ */
+static int
+context_derive_keys_rc4(struct krb5_ctx *ctx)
+{
+ struct crypto_hash *hmac;
+ char sigkeyconstant[] = "signaturekey";
+ int slen = strlen(sigkeyconstant) + 1; /* include null terminator */
+ struct hash_desc desc;
+ struct scatterlist sg[1];
+ int err;
+
+ dprintk("RPC: %s: entered\n", __func__);
+ /*
+ * derive cksum (aka Ksign) key
+ */
+ hmac = crypto_alloc_hash(ctx->gk5e->cksum_name, 0, CRYPTO_ALG_ASYNC);
+ if (IS_ERR(hmac)) {
+ dprintk("%s: error %ld allocating hash '%s'\n",
+ __func__, PTR_ERR(hmac), ctx->gk5e->cksum_name);
+ err = PTR_ERR(hmac);
+ goto out_err;
+ }
+
+ err = crypto_hash_setkey(hmac, ctx->Ksess, ctx->gk5e->keylength);
+ if (err)
+ goto out_err_free_hmac;
+
+ sg_init_table(sg, 1);
+ sg_set_buf(sg, sigkeyconstant, slen);
+
+ desc.tfm = hmac;
+ desc.flags = 0;
+
+ err = crypto_hash_init(&desc);
+ if (err)
+ goto out_err_free_hmac;
+
+ err = crypto_hash_digest(&desc, sg, slen, ctx->cksum);
+ if (err)
+ goto out_err_free_hmac;
+ /*
+ * allocate hash, and blkciphers for data and seqnum encryption
+ */
+ ctx->enc = crypto_alloc_blkcipher(ctx->gk5e->encrypt_name, 0,
+ CRYPTO_ALG_ASYNC);
+ if (IS_ERR(ctx->enc)) {
+ err = PTR_ERR(ctx->enc);
+ goto out_err_free_hmac;
+ }
+
+ ctx->seq = crypto_alloc_blkcipher(ctx->gk5e->encrypt_name, 0,
+ CRYPTO_ALG_ASYNC);
+ if (IS_ERR(ctx->seq)) {
+ crypto_free_blkcipher(ctx->enc);
+ err = PTR_ERR(ctx->seq);
+ goto out_err_free_hmac;
+ }
+
+ dprintk("RPC: %s: returning success\n", __func__);
+
+ err = 0;
+
+out_err_free_hmac:
+ crypto_free_hash(hmac);
+out_err:
+ dprintk("RPC: %s: returning %d\n", __func__, err);
+ return err;
+}
+