EVP Authenticated Encryption and Decryption - Revision history

Jwalton: Add additional information.

2019-06-05T04:48:04Z

Add additional information.

2019-06-05T04:46:58Z

Add additional information.

2019-04-30T15:07:32Z

2019-04-30T14:12:12Z

(Reformat code according to OpenSSL coding style and provide downloadable sample C files)

2017-11-01T13:22:06Z

Made GCM IV length a function parameter

2017-04-28T22:57:03Z

Add InfoBox link.

2017-04-28T22:52:01Z

Add links to all EVP articles.

2016-01-04T20:17:50Z

Correcting inferred definition of AEAD

2015-01-17T02:16:19Z

Added DocInclude template info for Authenticated Encryption and Decryption.

2015-01-09T22:37:40Z

Italicized Additional Authenticated Data

@@ Line 28: / Line 28: @@
 * You may optionally pass through an IV length using EVP_CIPHER_CTX_ctrl
 * AAD data is passed through in zero or more calls to EVP_EncryptUpdate, with the output buffer set to NULL
-* Once private data has been added, you cannot add AAD data
+* Once private data has been added using EVP_EncryptUpdate (non-NULL output buffer), you cannot add AAD data
 * After the EVP_EncryptFinal_ex call a new call to EVP_CIPHER_CTX_ctrl retrieves the tag

@@ Line 28: / Line 28: @@
 * You may optionally pass through an IV length using EVP_CIPHER_CTX_ctrl
 * AAD data is passed through in zero or more calls to EVP_EncryptUpdate, with the output buffer set to NULL
 * After the EVP_EncryptFinal_ex call a new call to EVP_CIPHER_CTX_ctrl retrieves the tag

@@ Line 54: / Line 54: @@
          handleErrors();
-     /* Set IV length if default 12 bytes (96 bits) is not appropriate */
+     /*
      if(1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, iv_len, NULL))
          handleErrors();
@@ Line 81: / Line 83: @@
       * this stage, but this does not occur in GCM mode
       */
-     if(1 != EVP_EncryptFinal_ex(ctx, ciphertext + len, &len)) handleErrors();
+     if(1 != EVP_EncryptFinal_ex(ctx, ciphertext + len, &len))
      ciphertext_len += len;
@@ Line 119: / Line 122: @@
      /* Create and initialise the context */
-     if(!(ctx = EVP_CIPHER_CTX_new())) handleErrors();
+     if(!(ctx = EVP_CIPHER_CTX_new()))
      /* Initialise the decryption operation. */
@@ Line 130: / Line 134: @@
      /* Initialise key and IV */
-     if(!EVP_DecryptInit_ex(ctx, NULL, NULL, key, iv)) handleErrors();
+     if(!EVP_DecryptInit_ex(ctx, NULL, NULL, key, iv))
      /*

@@ Line 31: / Line 31: @@
 <pre>
 int encrypt(unsigned char *plaintext, int plaintext_len, unsigned char *aad,
-	int aad_len, unsigned char *key, unsigned char *iv,
+	int aad_len, unsigned char *key, unsigned char *iv, int iv_len,
 	unsigned char *ciphertext, unsigned char *tag)
+{
@@ Line 49: / Line 49: @@
 	/* Set IV length if default 12 bytes (96 bits) is not appropriate */
-	if(1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 16, NULL))
+	if(1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, iv_len, NULL))
 		handleErrors();
@@ Line 98: / Line 98: @@
 int decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *aad,
 	int aad_len, unsigned char *tag, unsigned char *key, unsigned char *iv,
-	unsigned char *plaintext)
+	int iv_len, unsigned char *plaintext)
+{
 	EVP_CIPHER_CTX *ctx;
@@ Line 113: / Line 113: @@
 	/* Set IV length. Not necessary if this is 12 bytes (96 bits) */
-	if(!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 16, NULL))
+	if(!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, iv_len, NULL))
 		handleErrors();

@@ Line 1: / Line 1: @@
 {{DocInclude
 |Name=Authenticated Encryption and Decryption
-|Url=
+|Url=http://wiki.openssl.org/index.php/Manual:Evp(3)
 |Include=evp.h}}

@@ Line 308: / Line 308: @@
 ==See also==
 * [[EVP]]
 * [[Libcrypto API]]
 [[Category:Crypto API]]
 [[Category:C level]]
 [[Category:Examples]]

@@ Line 4: / Line 4: @@
 |Include=evp.h}}
-The EVP interface supports the ability to perform authenticated encryption and decryption. Authenticated encryption and decryption are also known as AEAD schemes. The AEAD schemes provide confidentiality by encrypting the data, and also provide authenticity assurances by creating a MAC tag over the encrypted data. The MAC tag will ensure the data is not accidentally altered or maliciously tampered during transmission and storage.
+The EVP interface supports the ability to perform authenticated encryption and decryption, as well as the option to attach unencrypted, associated data to the message. Such Authenticated-Encryption with Associated-Data (AEAD) schemes provide confidentiality by encrypting the data, and also provide authenticity assurances by creating a MAC tag over the encrypted data. The MAC tag will ensure the data is not accidentally altered or maliciously tampered during transmission and storage.
 There are a number of AEAD modes of operation. The modes include EAX, CCM and GCM mode. Using AEAD modes is nearly identical to using standard symmetric encryption modes like CBC, CFB and OFB modes.

@@ Line 1: / Line 1: @@
 The EVP interface supports the ability to perform authenticated encryption and decryption. Authenticated encryption and decryption are also known as AEAD schemes. The AEAD schemes provide confidentiality by encrypting the data, and also provide authenticity assurances by creating a MAC tag over the encrypted data. The MAC tag will ensure the data is not accidentally altered or maliciously tampered during transmission and storage.
@@ Line 5: / Line 10: @@
 As with standard symmetric encryption you will need to know the following:
-* Your algorithm (currently only AES is supported)
+* Algorithm (currently only AES is supported)
-* Your mode (currently only GCM and CCM are supported)
+* Mode (currently only GCM and CCM are supported)
-* Your key
+* Key
-* Your Initialisation Vector (IV)
+* Initialisation Vector (IV)
 In addition you can (optionally) provide some ''Additional Authenticated Data'' (AAD). The AAD data is not encrypted, and is typically passed to the recipient in plaintext along with the ciphertext. An example of AAD is the IP address and port number in a IP header used with IPsec.

@@ Line 10: / Line 10: @@
 * Your Initialisation Vector (IV)
-In addition you can (optionally) provide some "Additional Authenticated Data" (AAD). The AAD data is not encrypted, and is typically passed to the recipient in plaintext along with the ciphertext.
+In addition you can (optionally) provide some ''Additional Authenticated Data'' (AAD). The AAD data is not encrypted, and is typically passed to the recipient in plaintext along with the ciphertext. An example of AAD is the IP address and port number in a IP header used with IPsec.
 The output from the encryption operation will be the ciphertext, and a tag. The tag is subsequently used during the decryption operation to ensure that the ciphertext and AAD have not been tampered with.