diff --git a/params.c b/params.c
index 1053301..5191e4a 100644
--- a/params.c
+++ b/params.c
@@ -1,6 +1,8 @@
 #include <stdint.h>
 #include <string.h>
+
 #include "params.h"
+#include "xmss_core.h"
 
 int xmss_str_to_oid(uint32_t *oid, const char *s)
 {
@@ -237,7 +239,7 @@ int xmss_parse_oid(xmss_params *params, const uint32_t oid)
                          + params->d * params->wots_sig_bytes
                          + params->full_height * params->n);
     params->pk_bytes = 2 * params->n;
-    params->sk_bytes = 4 * params->n + params->index_bytes;
+    params->sk_bytes = xmss_core_sk_bytes(params);
 
     // TODO figure out sensible and legal values for this based on the above
     params->bds_k = 0;
@@ -455,7 +457,7 @@ int xmssmt_parse_oid(xmss_params *params, const uint32_t oid)
                          + params->d * params->wots_sig_bytes
                          + params->full_height * params->n);
     params->pk_bytes = 2 * params->n;
-    params->sk_bytes = 4 * params->n + params->index_bytes;
+    params->sk_bytes = xmssmt_core_sk_bytes(params);
 
     // TODO figure out sensible and legal values for this based on the above
     params->bds_k = 0;
diff --git a/params.h b/params.h
index 9155bcb..48478c7 100644
--- a/params.h
+++ b/params.h
@@ -26,7 +26,7 @@ typedef struct {
     unsigned int index_bytes;
     unsigned int sig_bytes;
     unsigned int pk_bytes;
-    unsigned int sk_bytes;
+    unsigned long long sk_bytes;
     unsigned int bds_k;
 } xmss_params;
 
diff --git a/xmss_core.c b/xmss_core.c
index 64bd32e..fda01c3 100644
--- a/xmss_core.c
+++ b/xmss_core.c
@@ -84,6 +84,16 @@ static void treehash(const xmss_params *params,
     memcpy(root, stack, params->n);
 }
 
+/**
+ * Given a set of parameters, this function returns the size of the secret key.
+ * This is implementation specific, as varying choices in tree traversal will
+ * result in varying requirements for state storage.
+ */
+unsigned long long xmss_core_sk_bytes(const xmss_params *params)
+{
+    return params->index_bytes + 4 * params->n;
+}
+
 /*
  * Generates a XMSS key pair for a given parameter set.
  * Format sk: [(32bit) index || SK_SEED || SK_PRF || PUB_SEED || root]
@@ -114,6 +124,16 @@ int xmss_core_sign(const xmss_params *params,
     return xmssmt_core_sign(params, sk, sm, smlen, m, mlen);
 }
 
+/**
+ * Given a set of parameters, this function returns the size of the secret key.
+ * This is implementation specific, as varying choices in tree traversal will
+ * result in varying requirements for state storage.
+ */
+unsigned long long xmssmt_core_sk_bytes(const xmss_params *params)
+{
+    return params->index_bytes + 4 * params->n;
+}
+
 /*
  * Generates a XMSSMT key pair for a given parameter set.
  * Format sk: [(ceil(h/8) bit) index || SK_SEED || SK_PRF || PUB_SEED]
diff --git a/xmss_core.h b/xmss_core.h
index e670dd8..251183b 100644
--- a/xmss_core.h
+++ b/xmss_core.h
@@ -3,6 +3,13 @@
 
 #include "params.h"
 
+/**
+ * Given a set of parameters, this function returns the size of the secret key.
+ * This is implementation specific, as varying choices in tree traversal will
+ * result in varying requirements for state storage.
+ */
+unsigned long long xmss_core_sk_bytes(const xmss_params *params);
+
 /*
  * Generates a XMSS key pair for a given parameter set.
  * Format sk: [(32bit) index || SK_SEED || SK_PRF || PUB_SEED || root]
@@ -29,6 +36,13 @@ int xmss_core_sign_open(const xmss_params *params,
                         const unsigned char *sm, unsigned long long smlen,
                         const unsigned char *pk);
 
+/**
+ * Given a set of parameters, this function returns the size of the secret key.
+ * This is implementation specific, as varying choices in tree traversal will
+ * result in varying requirements for state storage.
+ */
+unsigned long long xmssmt_core_sk_bytes(const xmss_params *params);
+
 /*
  * Generates a XMSSMT key pair for a given parameter set.
  * Format sk: [(ceil(h/8) bit) index || SK_SEED || SK_PRF || PUB_SEED]
diff --git a/xmss_core_fast.c b/xmss_core_fast.c
index 9971805..64e06c1 100644
--- a/xmss_core_fast.c
+++ b/xmss_core_fast.c
@@ -344,6 +344,16 @@ static void bds_round(const xmss_params *params,
     }
 }
 
+/**
+ * Given a set of parameters, this function returns the size of the secret key.
+ * This is implementation specific, as varying choices in tree traversal will
+ * result in varying requirements for state storage.
+ */
+unsigned long long xmss_core_sk_bytes(const xmss_params *params)
+{
+    return params->index_bytes + 4 * params->n;
+}
+
 /*
  * Generates a XMSS key pair for a given parameter set.
  * Format sk: [(32bit) idx || SK_SEED || SK_PRF || PUB_SEED || root]
@@ -483,6 +493,16 @@ int xmss_core_sign(const xmss_params *params,
     return 0;
 }
 
+/**
+ * Given a set of parameters, this function returns the size of the secret key.
+ * This is implementation specific, as varying choices in tree traversal will
+ * result in varying requirements for state storage.
+ */
+unsigned long long xmssmt_core_sk_bytes(const xmss_params *params)
+{
+    return params->index_bytes + 4 * params->n;
+}
+
 /*
  * Generates a XMSSMT key pair for a given parameter set.
  * Format sk: [(ceil(h/8) bit) idx || SK_SEED || SK_PRF || PUB_SEED || root]
diff --git a/xmss_core_fast.h b/xmss_core_fast.h
index 767dedd..699ed9e 100644
--- a/xmss_core_fast.h
+++ b/xmss_core_fast.h
@@ -31,6 +31,14 @@ void xmss_set_bds_state(bds_state *state, unsigned char *stack,
                         unsigned char *auth, unsigned char *keep,
                         treehash_inst *treehash, unsigned char *retain,
                         int next_leaf);
+
+/**
+ * Given a set of parameters, this function returns the size of the secret key.
+ * This is implementation specific, as varying choices in tree traversal will
+ * result in varying requirements for state storage.
+ */
+unsigned long long xmss_core_sk_bytes(const xmss_params *params);
+
 /**
  * Generates a XMSS key pair for a given parameter set.
  * Format sk: [(32bit) idx || SK_SEED || SK_PRF || PUB_SEED || root]
@@ -58,6 +66,13 @@ int xmss_core_sign_open(const xmss_params *params,
                         const unsigned char *sm, unsigned long long smlen,
                         const unsigned char *pk);
 
+/**
+ * Given a set of parameters, this function returns the size of the secret key.
+ * This is implementation specific, as varying choices in tree traversal will
+ * result in varying requirements for state storage.
+ */
+unsigned long long xmssmt_core_sk_bytes(const xmss_params *params);
+
 /*
  * Generates a XMSSMT key pair for a given parameter set.
  * Format sk: [(ceil(h/8) bit) idx || SK_SEED || SK_PRF || PUB_SEED || root]