add simple AES GCM code example

demos/evp/aesgcm.c

+/* Simple AES GCM test program, uses the same NIST data used for the FIPS
+ * self test but uses the application level EVP APIs.
+ */
+#include <stdio.h>
+#include <openssl/bio.h>
+#include <openssl/evp.h>
+
+/* AES-GCM test data from NIST public test vectors */
+
+static const unsigned char gcm_key[] = {
+	0xee,0xbc,0x1f,0x57,0x48,0x7f,0x51,0x92,0x1c,0x04,0x65,0x66,
+	0x5f,0x8a,0xe6,0xd1,0x65,0x8b,0xb2,0x6d,0xe6,0xf8,0xa0,0x69,
+	0xa3,0x52,0x02,0x93,0xa5,0x72,0x07,0x8f
+};
+
+static const unsigned char gcm_iv[] = {
+	0x99,0xaa,0x3e,0x68,0xed,0x81,0x73,0xa0,0xee,0xd0,0x66,0x84
+};
+
+static const unsigned char gcm_pt[] = {
+	0xf5,0x6e,0x87,0x05,0x5b,0xc3,0x2d,0x0e,0xeb,0x31,0xb2,0xea,
+	0xcc,0x2b,0xf2,0xa5
+};
+
+static const unsigned char gcm_aad[] = {
+	0x4d,0x23,0xc3,0xce,0xc3,0x34,0xb4,0x9b,0xdb,0x37,0x0c,0x43,
+	0x7f,0xec,0x78,0xde
+};
+
+static const unsigned char gcm_ct[] = {
+	0xf7,0x26,0x44,0x13,0xa8,0x4c,0x0e,0x7c,0xd5,0x36,0x86,0x7e,
+	0xb9,0xf2,0x17,0x36
+};
+
+static const unsigned char gcm_tag[] = {
+	0x67,0xba,0x05,0x10,0x26,0x2a,0xe4,0x87,0xd7,0x37,0xee,0x62,
+	0x98,0xf7,0x7e,0x0c
+};
+
+void aes_gcm_encrypt(void)
+	{
+	EVP_CIPHER_CTX *ctx;
+	int outlen, tmplen;
+	unsigned char outbuf[1024];
+	printf("AES GCM Encrypt:\n");
+	printf("Plaintext:\n");
+	BIO_dump_fp(stdout, gcm_pt, sizeof(gcm_pt));
+	ctx = EVP_CIPHER_CTX_new();
+	/* Set cipher type and mode */
+	EVP_EncryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL);
+	/* Set IV length if default 96 bits is not appropriate */
+	EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, sizeof(gcm_iv), NULL);
+	/* Initialise key and IV */
+	EVP_EncryptInit_ex(ctx, NULL, NULL, gcm_key, gcm_iv);
+	/* Zero or more calls to specify any AAD */
+	EVP_EncryptUpdate(ctx, NULL, &outlen, gcm_aad, sizeof(gcm_aad));
+	/* Encrypt plaintext */
+	EVP_EncryptUpdate(ctx, outbuf, &outlen, gcm_pt, sizeof(gcm_pt));
+	/* Output encrypted block */
+	printf("Ciphertext:\n");
+	BIO_dump_fp(stdout, outbuf, outlen);
+	/* Finalise: note get no output for GCM */
+	EVP_EncryptFinal_ex(ctx, outbuf, &outlen);
+	/* Get tag */
+	EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, 16, outbuf);
+	/* Output tag */
+	printf("Tag:\n");
+	BIO_dump_fp(stdout, outbuf, 16);
+	EVP_CIPHER_CTX_free(ctx);
+	}
+
+void aes_gcm_decrypt(void)
+	{
+	EVP_CIPHER_CTX *ctx;
+	int outlen, tmplen, rv;
+	unsigned char outbuf[1024];
+	printf("AES GCM Derypt:\n");
+	printf("Ciphertext:\n");
+	BIO_dump_fp(stdout, gcm_ct, sizeof(gcm_ct));
+	ctx = EVP_CIPHER_CTX_new();
+	/* Select cipher */
+	EVP_DecryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL);
+	/* Set IV length, omit for 96 bits */
+	EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, sizeof(gcm_iv), NULL);
+	/* Specify key and IV */
+	EVP_DecryptInit_ex(ctx, NULL, NULL, gcm_key, gcm_iv);
+#if 0
+	/* Set expected tag value. A restriction in OpenSSL 1.0.1c and earlier
+         * required the tag before any AAD or ciphertext */
+	EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, sizeof(gcm_tag), gcm_tag);
+#endif
+	/* Zero or more calls to specify any AAD */
+	EVP_DecryptUpdate(ctx, NULL, &outlen, gcm_aad, sizeof(gcm_aad));
+	/* Decrypt plaintext */
+	EVP_DecryptUpdate(ctx, outbuf, &outlen, gcm_ct, sizeof(gcm_ct));
+	/* Output decrypted block */
+	printf("Plaintext:\n");
+	BIO_dump_fp(stdout, outbuf, outlen);
+	/* Set expected tag value. Works in OpenSSL 1.0.1d and later */
+	EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, sizeof(gcm_tag), gcm_tag);
+	/* Finalise: note get no output for GCM */
+	rv = EVP_DecryptFinal_ex(ctx, outbuf, &outlen);
+	/* Print out return value. If this is not successful authentication
+	 * failed and plaintext is not trustworthy.
+	 */
+	printf("Tag Verify %s\n", rv > 0 ? "Successful!" : "Failed!");
+	EVP_CIPHER_CTX_free(ctx);
+	}
+
+int main(int argc, char **argv)
+	{
+	aes_gcm_encrypt();
+	aes_gcm_decrypt();
+	}