Libsodium sealed box with non-random ephemeral key

rand_five.c

#include <stdio.h>
#include <sodium.h>

const char *rand_five_implementation_name(void) {
  return "five";
}

uint32_t rand_five_random(void) {
  return 5;
}

void rand_five_buf(void * const buf, const size_t size) {
  for (int i = 0; i < size; i++) {
    ((unsigned char *)buf)[i] = 5;
  }
}

struct randombytes_implementation rand_five = {
  rand_five_implementation_name,
  rand_five_random,
  NULL,
  NULL,
  rand_five_buf
};

int main(int argc, char **argv) {
  if (sodium_init() < 0) {
      return 1;
  }

  randombytes_set_implementation(&rand_five);

  unsigned char privateKey[crypto_box_SECRETKEYBYTES];

  for (int i = 0; i < crypto_box_SECRETKEYBYTES; i++) {
    privateKey[i] = 1;
  }

  unsigned char publicKey[crypto_box_PUBLICKEYBYTES];

  if (crypto_scalarmult_base(publicKey, privateKey) != 0) {
    printf("Failed to calculate publicKey\n");
    return 1;
  }

  unsigned char message[64];
  for (int i = 0; i < 64; i++) {
    message[i] = 3;
  }

  unsigned char ciphertext[crypto_box_SEALBYTES + 64];
  if (crypto_box_seal(ciphertext, message, 64, publicKey) != 0) {
    printf("Failed calling crypto_box_seal\n");
    return 1;
  }

  for (int i = 0; i < crypto_box_SEALBYTES + 64; i++) {
    printf("%02x", ciphertext[i]);
  }
  printf("\n");

  return 0;
}

seal.c

#include <stdio.h>
#include <sodium.h>

int main(int argc, char **argv) {
  if (sodium_init() < 0) {
      return 1;
  }

  unsigned char privateKey[crypto_box_SECRETKEYBYTES];

  for (int i = 0; i < crypto_box_SECRETKEYBYTES; i++) {
    privateKey[i] = 1;
  }

  unsigned char publicKey[crypto_box_PUBLICKEYBYTES];

  if (crypto_scalarmult_base(publicKey, privateKey) != 0) {
    printf("Failed to calculate publicKey\n");
    return 1;
  }

  unsigned char message[64];
  for (int i = 0; i < 64; i++) {
    message[i] = 3;
  }

  unsigned char ciphertext[crypto_box_SEALBYTES + 64];
  if (crypto_box_seal(ciphertext, message, 64, publicKey) != 0) {
    printf("Failed calling crypto_box_seal\n");
    return 1;
  }

  for (int i = 0; i < crypto_box_SEALBYTES + 64; i++) {
    printf("%02x", ciphertext[i]);
  }
  printf("\n");

  return 0;
}

$ gcc -lsodium -o seal ./seal.c
$ ./seal
3462e0640728247a6f581e3812850d6edc3dcad1ea5d8184c072f62fb65cb357e27ffa8b76f41656bc66a0882c4d359568410665746d27462a700f01e314f382edd7aae9064879b0f8ba7b88866f88f5e4fbd7649c850541877f9f33ebd25d46d9cbcce09b69a9ba07f0eb1d105d4264