1 files changed, 41 insertions, 0 deletions
diff --git a/src/ltc/pk/ec25519/ec25519_crypto_ctx.c b/src/ltc/pk/ec25519/ec25519_crypto_ctx.c
new file mode 100644
index 00000000..e1efb301
--- /dev/null
+++ b/src/ltc/pk/ec25519/ec25519_crypto_ctx.c
@@ -0,0 +1,41 @@
+/* LibTomCrypt, modular cryptographic library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+#include "tomcrypt_private.h"
+
+/**
+  @file ec25519_crypto_ctx.c
+  curve25519 crypto context helper
+*/
+
+#ifdef LTC_CURVE25519
+
+int ec25519_crypto_ctx(unsigned char *out, unsigned long *outlen, unsigned char flag, const unsigned char *ctx, unsigned long ctxlen)
+{
+  unsigned char *buf = out;
+
+  const char *prefix = "SigEd25519 no Ed25519 collisions";
+  const unsigned long prefix_len = XSTRLEN(prefix);
+  const unsigned char ctxlen8 = (unsigned char)ctxlen;
+
+  if (ctxlen > 255u) return CRYPT_INPUT_TOO_LONG;
+  if (*outlen < prefix_len + 2u + ctxlen) return CRYPT_BUFFER_OVERFLOW;
+
+  XMEMCPY(buf, prefix, prefix_len);
+  buf += prefix_len;
+  XMEMCPY(buf, &flag, 1);
+  buf++;
+  XMEMCPY(buf, &ctxlen8, 1);
+  buf++;
+
+  if (ctxlen > 0u) {
+    LTC_ARGCHK(ctx != NULL);
+    XMEMCPY(buf, ctx, ctxlen);
+    buf += ctxlen;
+  }
+
+  *outlen = buf-out;
+
+  return CRYPT_OK;
+}
+
+#endif