iotests: skip 048 with qcow which doesn't support resize

[qemu.git] / qemu-img.texi

diff --git a/qemu-img.texi b/qemu-img.texi
index 50a2364e80e41ac223c68c6f483abe6e87103794..f335139217b0d112605e640509f8b9084c6ef7b1 100644 (file)
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -45,9 +45,17 @@ keys.
 
 @item --image-opts
 
-Indicates that the @var{filename} parameter is to be interpreted as a
+Indicates that the source @var{filename} parameter is to be interpreted as a
 full option string, not a plain filename. This parameter is mutually
-exclusive with the @var{-f} and @var{-F} parameters.
+exclusive with the @var{-f} parameter.
+
+@item --target-image-opts
+
+Indicates that the @var{output_filename} parameter(s) are to be interpreted as
+a full option string, not a plain filename. This parameter is mutually
+exclusive with the @var{-O} parameters. It is currently required to also use
+the @var{-n} parameter to skip image creation. This restriction may be relaxed
+in a future release.
 
 @item fmt
 is the disk image format. It is guessed automatically in most cases. See below
@@ -559,16 +567,29 @@ The use of encryption in qcow and qcow2 images is considered to be flawed by
 modern cryptography standards, suffering from a number of design problems:
 
 @itemize @minus
-@item The AES-CBC cipher is used with predictable initialization vectors based
+@item
+The AES-CBC cipher is used with predictable initialization vectors based
 on the sector number. This makes it vulnerable to chosen plaintext attacks
 which can reveal the existence of encrypted data.
-@item The user passphrase is directly used as the encryption key. A poorly
+@item
+The user passphrase is directly used as the encryption key. A poorly
 chosen or short passphrase will compromise the security of the encryption.
-@item In the event of the passphrase being compromised there is no way to
+@item
+In the event of the passphrase being compromised there is no way to
 change the passphrase to protect data in any qcow images. The files must
 be cloned, using a different encryption passphrase in the new file. The
 original file must then be securely erased using a program like shred,
 though even this is ineffective with many modern storage technologies.
+@item
+Initialization vectors used to encrypt sectors are based on the
+guest virtual sector number, instead of the host physical sector. When
+a disk image has multiple internal snapshots this means that data in
+multiple physical sectors is encrypted with the same initialization
+vector. With the CBC mode, this opens the possibility of watermarking
+attacks if the attack can collect multiple sectors encrypted with the
+same IV and some predictable data. Having multiple qcow2 images with
+the same passphrase also exposes this weakness since the passphrase
+is directly used as the key.
 @end itemize
 
 Use of qcow / qcow2 encryption is thus strongly discouraged. Users are