diff --git a/include/bravais.h b/include/bravais.h
index 39215fe..f795dd6 100644
--- a/include/bravais.h
+++ b/include/bravais.h
@@ -19,6 +19,11 @@ extern "C" {
 
 #define BRAVAIS_NO_TIMEOUT UINT64_MAX
 
+#define BRAVAIS_MAX_DATAGRAM_SIZE 1500
+#define BRAVAIS_MAX_PLAINTEXT_SIZE 65535
+
+#define BRAVAIS_KEY_LENGTH 32 // For X25519 private and public - do PQC later
+
 typedef enum {
     // Error codes; Generally <0 = error, 0 = success
     BRAVAIS_EMPTY = 1, // Nothing to emit right now
diff --git a/src/util/buf.c b/src/util/buf.c
new file mode 100644
index 0000000..4664475
--- /dev/null
+++ b/src/util/buf.c
@@ -0,0 +1,208 @@
+#include "buf.h"
+#include "intutils.h"
+
+// Internal claim functions to avoid code duplication in the cursor functions
+static const uint8_t* rcur_claim(bravais_rcur_t* cur, size_t n) {
+    if (cur->failed || n > cur->len - cur->pos) {
+        cur->failed = true;
+        return nullptr;
+    }
+
+    if (cur->base == nullptr) {
+        return nullptr;
+    }
+
+    const uint8_t* start = cur->base + cur->pos;
+    cur->pos += n;
+
+    return start;
+}
+
+static uint8_t* wcur_claim(bravais_wcur_t* cur, size_t n) {
+    if (cur->failed || n > cur->len - cur->pos) {
+        cur->failed = true;
+        return nullptr;
+    }
+
+    if (cur->base == nullptr) {
+        return nullptr;
+    }
+
+    uint8_t* start = cur->base + cur->pos;
+    cur->pos += n;
+
+    return start;
+}
+
+void bravais_rcur_init(bravais_rcur_t* cur, const uint8_t* buf, size_t len) {
+    cur->buf = buf;
+    cur->len = len;
+    cur->pos = 0;
+    cur->failed = false;
+}
+
+uint8_t bravais_rcur_u8(bravais_rcur_t* cur) {
+    const uint8_t* ptr = rcur_claim(cur, 1);
+    if (ptr == nullptr) {
+        return 0;
+    }
+
+    return ptr[0];
+}
+
+uint16_t bravais_rcur_u16(bravais_rcur_t* cur) {
+    const uint8_t* ptr = rcur_claim(cur, 2);
+    if (ptr == nullptr) {
+        return 0;
+    }
+
+    // Assemble from bytes in big-endian order
+    uint16_t val = (uint16_t)((ptr[0] << 8) | ptr[1]);
+
+    return val;
+}
+
+uint32_t bravais_rcur_u32(bravais_rcur_t* cur) {
+    const uint8_t* ptr = rcur_claim(cur, 4);
+    if (ptr == nullptr) {
+        return 0;
+    }
+
+    // Assemble from bytes in big-endian order
+    uint32_t val = (uint32_t)((ptr[0] << 24) | (ptr[1] << 16) | (ptr[2] << 8) | ptr[3]);
+
+    return val;
+}
+
+uint64_t bravais_rcur_u64(bravais_rcur_t* cur) {
+    const uint8_t* ptr = rcur_claim(cur, 8);
+    if (ptr == nullptr) {
+        return 0;
+    }
+
+    // Assemble from bytes in big-endian order
+    uint64_t val = ((uint64_t)ptr[0] << 56)
+                 | ((uint64_t)ptr[1] << 48)
+                 | ((uint64_t)ptr[2] << 40)
+                 | ((uint64_t)ptr[3] << 32)
+                 | ((uint64_t)ptr[4] << 24)
+                 | ((uint64_t)ptr[5] << 16)
+                 | ((uint64_t)ptr[6] << 8)
+                 | ((uint64_t)ptr[7]);
+
+    return val;
+}
+
+void bravais_rcur_bytes(bravais_rcur_t* cur, uint8_t* outBuf, size_t len) {
+    if (len <= 0) { return; }
+
+    const uint8_t* ptr = rcur_claim(cur, len);
+    if (ptr == nullptr) {
+        memset(outBuf, 0, len);
+        return;
+    }
+
+    memcpy(outBuf, ptr, len);
+}
+
+const uint8_t* bravais_rcur_slice(bravais_rcur_t* cur, size_t len) {
+    return rcur_claim(cur, len);
+}
+
+void bravais_rcur_skip(bravais_rcur_t* cur, size_t len) {
+    (void)rcur_claim(cur, len);
+}
+
+size_t bravais_rcur_remaining(const bravais_rcur_t* cur) {
+    if (cur->failed) {
+        return 0;
+    }
+
+    return cur->len - cur->pos;
+}
+
+bool bravais_rcur_ok(const bravais_rcur_t* cur) {
+    return !cur->failed;
+}
+
+void bravais_wcur_init(bravais_wcur_t* cur, uint8_t* buf, size_t len) {
+    cur->buf = buf;
+    cur->len = len;
+    cur->pos = 0;
+    cur->failed = false;
+}
+
+void bravais_wcur_u8(bravais_wcur_t* cur, uint8_t val) {
+    uint8_t* ptr = wcur_claim(cur, 1);
+    if (ptr == nullptr) {
+        return;
+    }
+
+    ptr[0] = val;
+}
+
+void bravais_wcur_u16(bravais_wcur_t* cur, uint16_t val) {
+    uint8_t* ptr = wcur_claim(cur, 2);
+    if (ptr == nullptr) {
+        return;
+    }
+
+    // Assemble into bytes in big-endian order
+    ptr[0] = (uint8_t)(val >> 8);
+    ptr[1] = (uint8_t)(val);
+}
+
+void bravais_wcur_u32(bravais_wcur_t* cur, uint32_t val) {
+    uint8_t* ptr = wcur_claim(cur, 4);
+    if (ptr == nullptr) {
+        return;
+    }
+
+    ptr[0] = (uint8_t)(val >> 24);
+    ptr[1] = (uint8_t)(val >> 16);
+    ptr[2] = (uint8_t)(val >> 8);
+    ptr[3] = (uint8_t)(val);
+}
+
+void bravais_wcur_u64(bravais_wcur_t* cur, uint64_t val) {
+    uint8_t* ptr = wcur_claim(cur, 8);
+    if (ptr == nullptr) {
+        return;
+    }
+
+    ptr[0] = (uint8_t)(val >> 56);
+    ptr[1] = (uint8_t)(val >> 48);
+    ptr[2] = (uint8_t)(val >> 40);
+    ptr[3] = (uint8_t)(val >> 32);
+    ptr[4] = (uint8_t)(val >> 24);
+    ptr[5] = (uint8_t)(val >> 16);
+    ptr[6] = (uint8_t)(val >> 8);
+    ptr[7] = (uint8_t)(val);
+}
+
+void bravais_wcur_bytes(bravais_wcur_t* cur, const uint8_t* val, size_t len) {
+    if (len <= 0) { return; }
+
+    uint8_t* ptr = wcur_claim(cur, len);
+    if (ptr == nullptr) {
+        return;
+    }
+
+    memcpy(ptr, val, len);
+}
+
+size_t bravais_wcur_written(const bravais_wcur_t* cur) {
+    return cur->pos;
+}
+
+size_t bravais_wcur_remaining(const bravais_wcur_t* cur) {
+    if (cur->failed) {
+        return 0;
+    }
+
+    return cur->len - cur->pos;
+}
+
+bool bravais_wcur_ok(const bravais_wcur_t* cur) {
+    return !cur->failed;
+}
diff --git a/src/util/buf.h b/src/util/buf.h
new file mode 100644
index 0000000..37ca01e
--- /dev/null
+++ b/src/util/buf.h
@@ -0,0 +1,54 @@
+// buf.h
+// Bounds-checked cursors over a buffer/byte range.
+//
+// Sticky-failure flags - if an op runs past the end, it sets a "failed" flag and returns a no-op zero value.
+// Check with bravais_<w/r>cur_ok() at the end of a serialization/deserialization operation to see if it succeeded.
+//
+// Multi-byte integer serialization is big-endian, as per the network order convention. Variable-length might live somewhere else later.
+//
+// A slice gets returned by bravais_rcur_slice() and points into the underlying buffer.
+
+#ifndef BRAVAIS_BUF_H
+#define BRAVAIS_BUF_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+typedef struct {
+    const uint8_t* buf;
+    size_t len;
+    size_t pos;
+    bool failed;
+} bravais_rcur_t;
+
+typedef struct {
+    uint8_t* buf;
+    size_t len;
+    size_t pos;
+    bool failed;
+} bravais_wcur_t;
+
+// Reader cursor functions
+void bravais_rcur_init(bravais_rcur_t* cur, const uint8_t* buf, size_t len);
+uint8_t bravais_rcur_u8(bravais_rcur_t* cur);
+uint16_t bravais_rcur_u16(bravais_rcur_t* cur);
+uint32_t bravais_rcur_u32(bravais_rcur_t* cur);
+uint64_t bravais_rcur_u64(bravais_rcur_t* cur);
+void bravais_rcur_bytes(bravais_rcur_t* cur, uint8_t* outBuf, size_t len); // zero-fills on failure
+const uint8_t* bravais_rcur_slice(bravais_rcur_t* cur, size_t len); // returns NULL on failure, borrows
+void bravais_rcur_skip(bravais_rcur_t* cur, size_t len); // skips bytes, sets failed on overflow
+size_t bravais_rcur_remaining(const bravais_rcur_t* cur); // How many bytes are left to read
+bool bravais_rcur_ok(const bravais_rcur_t* cur);
+
+// Writer cursor functions
+void bravais_wcur_init(bravais_wcur_t* cur, uint8_t* buf, size_t len);
+void bravais_wcur_u8(bravais_wcur_t* cur, uint8_t val);
+void bravais_wcur_u16(bravais_wcur_t* cur, uint16_t val);
+void bravais_wcur_u32(bravais_wcur_t* cur, uint32_t val);
+void bravais_wcur_u64(bravais_wcur_t* cur, uint64_t val);
+void bravais_wcur_bytes(bravais_wcur_t* cur, const uint8_t* val, size_t len);
+size_t bravais_wcur_written(const bravais_wcur_t* cur); // How many bytes have been written so far
+size_t bravais_wcur_remaining(const bravais_wcur_t* cur); // How many bytes are left to write
+bool bravais_wcur_ok(const bravais_wcur_t* cur);
+
+#endif // BRAVAIS_BUF_H
diff --git a/src/util/intutils.h b/src/util/intutils.h
new file mode 100644
index 0000000..fc1cd30
--- /dev/null
+++ b/src/util/intutils.h
@@ -0,0 +1,32 @@
+// intutils.h
+// Utilities for integers (byte order flipping for now)
+
+#ifndef BRAVAIS_INTUTILS_H
+#define BRAVAIS_INTUTILS_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+static inline uint16_t bravais_bswap16(uint16_t x) {
+    return (uint16_t)((x << 8) | (x >> 8));
+}
+
+static inline uint32_t bravais_bswap32(uint32_t x) {
+    return (uint32_t)(((x & 0x000000FF) << 24) |
+           ((x & 0x0000FF00) << 8) |
+           ((x & 0x00FF0000) >> 8) |
+           ((x & 0xFF000000) >> 24));
+}
+
+static inline uint64_t bravais_bswap64(uint64_t x) {
+    return (uint64_t)(((x & 0x00000000000000FFULL) << 56) |
+           ((x & 0x000000000000FF00ULL) << 40) |
+           ((x & 0x0000000000FF0000ULL) << 24) |
+           ((x & 0x00000000FF000000ULL) << 8) |
+           ((x & 0x000000FF00000000ULL) >> 8) |
+           ((x & 0x0000FF0000000000ULL) >> 24) |
+           ((x & 0x00FF000000000000ULL) >> 40) |
+           ((x & 0xFF00000000000000ULL) >> 56));
+}
+
+#endif // BRAVAIS_INTUTILS_H