crypto: echainiv - Add encrypted chain IV generator

This patch adds a new AEAD IV generator echainiv.  It is intended
to replace the existing skcipher IV generator eseqiv.

If the underlying AEAD algorithm is using the old AEAD interface,
then echainiv will simply use its IV generator.

Otherwise, echainiv will encrypt a counter just like eseqiv but
it'll first xor it against a previously stored IV similar to
chainiv.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/Kconfig

@@ -227,6 +227,16 @@ config CRYPTO_SEQIV
 	  This IV generator generates an IV based on a sequence number by
 	  xoring it with a salt.  This algorithm is mainly useful for CTR
 
+config CRYPTO_ECHAINIV
+	tristate "Encrypted Chain IV Generator"
+	select CRYPTO_AEAD
+	select CRYPTO_NULL
+	select CRYPTO_RNG
+	help
+	  This IV generator generates an IV based on the encryption of
+	  a sequence number xored with a salt.  This is the default
+	  algorithm for CBC.
+
 comment "Block modes"
 
 config CRYPTO_CBC

crypto/Makefile

@@ -21,6 +21,7 @@ obj-$(CONFIG_CRYPTO_BLKCIPHER2) += crypto_blkcipher.o
 obj-$(CONFIG_CRYPTO_BLKCIPHER2) += chainiv.o
 obj-$(CONFIG_CRYPTO_BLKCIPHER2) += eseqiv.o
 obj-$(CONFIG_CRYPTO_SEQIV) += seqiv.o
+obj-$(CONFIG_CRYPTO_ECHAINIV) += echainiv.o
 
 crypto_hash-y += ahash.o
 crypto_hash-y += shash.o