PARQUET-1398: move iv_prefix to Algorithms (#103)

diff --git a/src/main/thrift/parquet.thrift b/src/main/thrift/parquet.thrift
index 3a26579..010c24c 100644
--- a/src/main/thrift/parquet.thrift
+++ b/src/main/thrift/parquet.thrift
@@ -899,11 +899,22 @@
 struct AesGcmV1 {
   /** Retrieval metadata of AAD used for encryption of pages and structures **/
   1: optional binary aad_metadata
+
+  /** If file IVs are comprised of a fixed part, and variable parts
+   *  (e.g. counter), keep the fixed part here **/
+  2: optional binary iv_prefix
+ 
 }
 
 struct AesGcmCtrV1 {
   /** Retrieval metadata of AAD used for encryption of structures **/
   1: optional binary aad_metadata
+
+  /** If file IVs are comprised of a fixed part, and variable parts
+   *  (e.g. counter), keep the fixed part here **/
+  2: optional binary gcm_iv_prefix
+
+  3: optional binary ctr_iv_prefix
 }
 
 union EncryptionAlgorithm {
@@ -923,10 +934,5 @@
 
   /** Offset of Parquet footer (encrypted, or plaintext) **/
   4: required i64 footer_offset
-  
-  /** If file IVs are comprised of a fixed part,
-   *  and variable parts (random or counter), keep the fixed
-   *  part here **/
-  5: optional binary iv_prefix
 }