### Complete SPHINCS+ Sign and Verify Example in C

Source: https://context7.com/sphincs/sphincsplus/llms.txt

This C code demonstrates the full signing and verification process using SPHINCS+. It includes key generation, message signing, signature verification, and checks for message integrity. It also includes a test for tampering detection.

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "api.h"
#include "params.h"
#include "randombytes.h"

#define MESSAGE_LEN 1024

int main(void) {
    int ret = 0;

    /* Allocate key buffers */
    unsigned char pk[SPX_PK_BYTES];
    unsigned char sk[SPX_SK_BYTES];

    /* Allocate message buffers */
    unsigned char *message = malloc(MESSAGE_LEN);
    unsigned char *sm = malloc(SPX_BYTES + MESSAGE_LEN);
    unsigned char *mout = malloc(SPX_BYTES + MESSAGE_LEN);
    unsigned long long smlen, mlen;

    if (!message || !sm || !mout) {
        printf("Memory allocation failed!\n");
        ret = -1;
        goto cleanup;
    }

    /* Generate random message */
    randombytes(message, MESSAGE_LEN);
    printf("Generated %d byte random message.\n", MESSAGE_LEN);

    /* Step 1: Generate key pair */
    printf("Generating SPHINCS+ key pair...\n");
    if (crypto_sign_keypair(pk, sk) != 0) {
        printf("ERROR: Key generation failed!\n");
        ret = -1;
        goto cleanup;
    }
    printf("  Public key:  %d bytes\n", SPX_PK_BYTES);
    printf("  Secret key:  %d bytes\n", SPX_SK_BYTES);

    /* Step 2: Sign the message */
    printf("Signing message...\n");
    if (crypto_sign(sm, &smlen, message, MESSAGE_LEN, sk) != 0) {
        printf("ERROR: Signing failed!\n");
        ret = -1;
        goto cleanup;
    }
    printf("  Signature:   %d bytes\n", SPX_BYTES);
    printf("  Total output: %llu bytes (sig + msg)\n", smlen);

    /* Step 3: Verify signature and extract message */
    printf("Verifying signature...\n");
    if (crypto_sign_open(mout, &mlen, sm, smlen, pk) != 0) {
        printf("ERROR: Verification failed!\n");
        ret = -1;
        goto cleanup;
    }

    /* Step 4: Confirm extracted message matches original */
    if (mlen != MESSAGE_LEN || memcmp(message, mout, MESSAGE_LEN) != 0) {
        printf("ERROR: Message mismatch!\n");
        ret = -1;
        goto cleanup;
    }

    printf("SUCCESS: Signature verified, message recovered correctly.\n");

    /* Test tampering detection */
    printf("\nTesting tampering detection...\n");
    sm[SPX_BYTES / 2] ^= 0xFF;  /* Corrupt middle of signature */
    if (crypto_sign_open(mout, &mlen, sm, smlen, pk) == 0) {
        printf("ERROR: Tampered signature was incorrectly accepted!\n");
        ret = -1;
    } else {
        printf("SUCCESS: Tampered signature correctly rejected.\n");
    }

cleanup:
    free(message);
    free(sm);
    free(mout);
    return ret;
}

```

--------------------------------

### Build Reference Implementation with Haraka

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Compile the reference implementation with Haraka, 192-bit security, and the fast signing variant. Ensure you are in the 'ref' directory and run 'make clean' before building.

```bash
make clean
make PARAMS=sphincs-haraka-192f test/spx
./test/spx
```

--------------------------------

### Run Benchmark for Reference Implementation

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Build and execute the benchmark for the reference implementation using the SHA-256, 128-bit security, fast variant. This measures key generation, signing, and verification performance.

```bash
cd ref
make PARAMS=sphincs-sha2-128f test/benchmark
./test/benchmark
```

--------------------------------

### Build Reference Implementation with SHA-256

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Compile the reference implementation with SHA-256, 128-bit security, and the fast signing variant. Ensure you are in the 'ref' directory and run 'make clean' before building.

```bash
cd ref
make clean
make PARAMS=sphincs-sha2-128f test/spx
./test/spx
```

--------------------------------

### Build Reference Implementation with SHAKE256

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Compile the reference implementation with SHAKE256, 256-bit security, and small signatures. Ensure you are in the 'ref' directory and run 'make clean' before building.

```bash
make clean
make PARAMS=sphincs-shake-256s test/spx
./test/spx
```

--------------------------------

### Run Benchmark for AVX2-Optimized Implementation

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Build and execute the benchmark for the AVX2-optimized SHA-256 implementation with the fast signing variant. This measures key generation, signing, and verification performance.

```bash
cd ../sha2-avx2
make PARAMS=sphincs-sha2-256f test/benchmark
./test/benchmark
```

--------------------------------

### Build Haraka with AES-NI Acceleration

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Compile the Haraka implementation with AES-NI acceleration, using the 256-bit security small signatures variant. Navigate to the 'haraka-aesni' directory and run 'make clean' before building.

```bash
cd ../haraka-aesni
make clean
make PARAMS=sphincs-haraka-256s test/spx
./test/spx
```

--------------------------------

### Build Optimized AVX2 SHA-256 Implementation

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Compile the optimized AVX2 SHA-256 implementation with the fast signing variant. Navigate to the 'sha2-avx2' directory and run 'make clean' before building.

```bash
cd ../sha2-avx2
make clean
make PARAMS=sphincs-sha2-256f test/spx
./test/spx
```

--------------------------------

### Build Optimized AVX2 SHAKE Implementation

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Compile the optimized AVX2 SHAKE implementation with the 128-bit security fast signing variant. Navigate to the 'shake-avx2' directory and run 'make clean' before building.

```bash
cd ../shake-avx2
make clean
make PARAMS=sphincs-shake-128f test/spx
./test/spx
```

--------------------------------

### Generate Known Answer Tests (KAT) for Reference Implementation

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Build the KAT generator for the reference implementation with SHA-256, 128-bit security, fast variant. This requires OpenSSL for a deterministic random number generator and produces test vector files.

```bash
cd ref
make PARAMS=sphincs-sha2-128f PQCgenKAT_sign
./PQCgenKAT_sign
```

--------------------------------

### Sign Message (Combined Signature + Message)

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Creates a signature for a message and combines it with the original message into a single output buffer. The output format is signature followed by the message. Requires allocating sufficient buffer space for both.

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "api.h"
#include "params.h"
#include "randombytes.h"

int main(void) {
    unsigned char pk[SPX_PK_BYTES];
    unsigned char sk[SPX_SK_BYTES];

    /* Message to sign */
    unsigned char message[] = "Hello, post-quantum world!";
    unsigned long long mlen = sizeof(message) - 1;

    /* Allocate buffer for signature + message */
    unsigned char *sm = malloc(SPX_BYTES + mlen);
    unsigned long long smlen;

    /* Generate keys */
    crypto_sign_keypair(pk, sk);

    /* Sign the message - output is signature || message */
    if (crypto_sign(sm, &smlen, message, mlen, sk) != 0) {
        printf("Signing failed!\n");
        free(sm);
        return -1;
    }

    printf("Message signed successfully.\n");
    printf("Original message length: %llu bytes\n", mlen);
    printf("Signed message length: %llu bytes\n", smlen);
    printf("Signature size: %d bytes (%.2f KiB)\n", SPX_BYTES, SPX_BYTES / 1024.0);

    /* Output (for sphincs-sha2-128f):
     * Message signed successfully.
     * Original message length: 26 bytes
     * Signed message length: 17114 bytes
     * Signature size: 17088 bytes (16.69 KiB)
     */

    free(sm);
    return 0;
}
```

--------------------------------

### Verify SHA256 Checksums for KAT Files

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Verify the SHA256 checksums of the generated KAT files against known good values. This command should be run from the directory containing the SHA256SUMS file.

```bash
cd ..
sha256sum -c SHA256SUMS
```

--------------------------------

### Deterministic Key Generation from Seed

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Generates a SPHINCS+ key pair deterministically from a provided seed. The seed must be 3*SPX_N bytes long. This ensures reproducible key generation.

```c
#include <string.h>
#include "api.h"
#include "params.h"

int main(void) {
    unsigned char pk[SPX_PK_BYTES];
    unsigned char sk[SPX_SK_BYTES];
    unsigned char seed[CRYPTO_SEEDBYTES];  /* 3 * SPX_N bytes */

    /* Initialize seed with deterministic values (in practice, use secure random) */
    memset(seed, 0x42, CRYPTO_SEEDBYTES);

    /* Generate key pair from seed - same seed always produces same keys */
    if (crypto_sign_seed_keypair(pk, sk, seed) != 0) {
        return -1;
    }

    printf("Deterministic key pair generated from seed.\n");
    printf("Seed size: %llu bytes\n", crypto_sign_seedbytes());
    /* Output:
     * Deterministic key pair generated from seed.
     * Seed size: 48 bytes (for 128-bit security)
     */
    return 0;
}
```

--------------------------------

### Query SPHINCS+ Parameter Sizes

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Retrieves the byte sizes for SPHINCS+ cryptographic parameters like secret key, public key, and signature at runtime. This is essential for correct buffer allocation.

```c
#include <stdio.h>
#include "api.h"

int main(void) {
    printf("SPHINCS+ Parameter Sizes:\n");
    printf("========================\n");
    printf("Secret key:  %llu bytes\n", crypto_sign_secretkeybytes());
    printf("Public key:  %llu bytes\n", crypto_sign_publickeybytes());
    printf("Signature:   %llu bytes\n", crypto_sign_bytes());
    printf("Seed:        %llu bytes\n", crypto_sign_seedbytes());

    /* Output (for sphincs-sha2-128f):
     * SPHINCS+ Parameter Sizes:
     * ========================
     * Secret key:  64 bytes
     * Public key:  32 bytes
     * Signature:   17088 bytes
     * Seed:        48 bytes
     *
     * Output (for sphincs-sha2-256s):
     * Secret key:  128 bytes
     * Public key:  64 bytes
     * Signature:   29792 bytes
     * Seed:        96 bytes
     */
    return 0;
}

```

--------------------------------

### Generate SPHINCS+ Key Pair

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Generates a random SPHINCS+ public and secret key pair. The secret key includes SK_SEED, SK_PRF, PUB_SEED, and root, while the public key contains PUB_SEED and root.

```c
#include <stdio.h>
#include <string.h>
#include "api.h"
#include "params.h"
#include "randombytes.h"

int main(void) {
    unsigned char pk[SPX_PK_BYTES];  /* Public key buffer */
    unsigned char sk[SPX_SK_BYTES];  /* Secret key buffer */

    /* Generate a random SPHINCS+ key pair */
    if (crypto_sign_keypair(pk, sk) != 0) {
        printf("Key generation failed!\n");
        return -1;
    }

    printf("Key pair generated successfully.\n");
    printf("Public key size: %d bytes\n", SPX_PK_BYTES);
    printf("Secret key size: %d bytes\n", SPX_SK_BYTES);

    /* Output:
     * Key pair generated successfully.
     * Public key size: 32 bytes (for 128-bit security)
     * Secret key size: 64 bytes (for 128-bit security)
     */
    return 0;
}
```

--------------------------------

### Create Detached SPHINCS+ Signature

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Generates a detached signature for a given message using a private key. The signature can be stored or transmitted separately from the message. Ensure necessary headers are included.

```c
#include <stdio.h>
#include <stdlib.h>
#include "api.h"
#include "params.h"
#include "randombytes.h"

int main(void) {
    unsigned char pk[SPX_PK_BYTES];
    unsigned char sk[SPX_SK_BYTES];
    unsigned char sig[SPX_BYTES];  /* Detached signature buffer */
    size_t siglen;

    /* Message to sign */
    unsigned char message[] = "Sign this document";
    size_t mlen = sizeof(message) - 1;

    /* Generate keys */
    crypto_sign_keypair(pk, sk);

    /* Create detached signature */
    if (crypto_sign_signature(sig, &siglen, message, mlen, sk) != 0) {
        printf("Signature generation failed!\n");
        return -1;
    }

    printf("Detached signature created.\n");
    printf("Signature length: %zu bytes\n", siglen);
    printf("Message and signature can be transmitted separately.\n");

    /* Output:
     * Detached signature created.
     * Signature length: 17088 bytes (for sphincs-sha2-128f)
     * Message and signature can be transmitted separately.
     */
    return 0;
}

```

--------------------------------

### Verify and Extract Message from Combined SPHINCS+ Signature

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Verifies a combined signature-message buffer and extracts the original message. This is useful when the signature and message are transmitted together. It also includes a test for invalid signatures.

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "api.h"
#include "params.h"
#include "randombytes.h"

int main(void) {
    unsigned char pk[SPX_PK_BYTES];
    unsigned char sk[SPX_SK_BYTES];

    unsigned char message[] = "Important document content";
    unsigned long long mlen = sizeof(message) - 1;

    unsigned char *sm = malloc(SPX_BYTES + mlen);
    unsigned char *mout = malloc(SPX_BYTES + mlen);  /* Buffer for extracted message */
    unsigned long long smlen, moutlen;

    /* Generate keys and sign */
    crypto_sign_keypair(pk, sk);
    crypto_sign(sm, &smlen, message, mlen, sk);

    /* Verify and extract message */
    if (crypto_sign_open(mout, &moutlen, sm, smlen, pk) != 0) {
        printf("Verification failed!\n");
        free(sm);
        free(mout);
        return -1;
    }

    printf("Signature verified and message extracted.\n");
    printf("Extracted message length: %llu bytes\n", moutlen);
    printf("Message matches original: %s\n",
           (memcmp(message, mout, mlen) == 0) ? "YES" : "NO");

    /* Test invalid signature */
    sm[0] ^= 1;  /* Flip one bit in signature */
    if (crypto_sign_open(mout, &moutlen, sm, smlen, pk) != 0) {
        printf("Invalid signature correctly rejected.\n");
    }

    /* Output:
     * Signature verified and message extracted.
     * Extracted message length: 26 bytes
     * Message matches original: YES
     * Invalid signature correctly rejected.
     */

    free(sm);
    free(mout);
    return 0;
}

```

--------------------------------

### Verify Detached SPHINCS+ Signature

Source: https://context7.com/sphincs/sphincsplus/llms.txt

Verifies a detached signature against a message using a public key. This function checks the integrity of the signature and the message. It also demonstrates rejection of tampered messages.

```c
#include <stdio.h>
#include "api.h"
#include "params.h"
#include "randombytes.h"

int main(void) {
    unsigned char pk[SPX_PK_BYTES];
    unsigned char sk[SPX_SK_BYTES];
    unsigned char sig[SPX_BYTES];
    size_t siglen;

    unsigned char message[] = "Verify this message";
    size_t mlen = sizeof(message) - 1;

    /* Generate keys and sign */
    crypto_sign_keypair(pk, sk);
    crypto_sign_signature(sig, &siglen, message, mlen, sk);

    /* Verify the detached signature */
    if (crypto_sign_verify(sig, siglen, message, mlen, pk) != 0) {
        printf("Signature verification FAILED!\n");
        return -1;
    }
    printf("Signature verified successfully.\n");

    /* Test with tampered message */
    unsigned char tampered[] = "Verify this messag!";  /* Changed last char */
    if (crypto_sign_verify(sig, siglen, tampered, mlen, pk) != 0) {
        printf("Tampered message correctly rejected.\n");
    }

    /* Output:
     * Signature verified successfully.
     * Tampered message correctly rejected.
     */
    return 0;
}

```

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