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Correct and simplify block-based cipher modes

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OFB and CFB are streaming modes. XTS is a not a cipher mode but it
doesn't use a separate padding step. This leaves only CBC as a block
cipher mode that needs a padding step.

Since CBC is the only mode that uses a separate padding step, and is
likely to remain the only mode in the future, encode the padding mode
directly in the algorithm constant, rather than building up an
algorithm value from a chaining mode and a padding mode. This greatly
simplifies the interface as well as some parts of the implementation.
This commit is contained in:
Gilles Peskine
2018-08-21 14:02:45 +02:00
parent 81ba4abb02
commit daea26f70f
5 changed files with 132 additions and 202 deletions
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43
scripts/generate_psa_constants.py
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@ -47,34 +47,11 @@ static int psa_snprint_key_type(char *buffer, size_t buffer_size,
return required_size;
}
static void append_padding_mode(char **buffer, size_t buffer_size,
size_t *required_size,
psa_algorithm_t padding_mode)
{
size_t n;
append(buffer, buffer_size, required_size, " | ", 3);
switch (padding_mode) {
%(padding_mode_cases)s
default:
n = snprintf(*buffer, buffer_size - *required_size,
"0x%%08lx", (unsigned long) padding_mode);
if (n < buffer_size - *required_size) *buffer += n;
*required_size += n;
break;
}
}
static int psa_snprint_algorithm(char *buffer, size_t buffer_size,
psa_algorithm_t alg)
{
size_t required_size = 0;
psa_algorithm_t padding_mode = -1;
psa_algorithm_t alg_without_padding = alg;
if (PSA_ALG_IS_CIPHER(alg) && PSA_ALG_IS_BLOCK_CIPHER(alg)) {
padding_mode = alg & PSA_ALG_BLOCK_CIPHER_PADDING_MASK;
alg_without_padding = alg & ~PSA_ALG_BLOCK_CIPHER_PADDING_MASK;
}
switch (alg_without_padding) {
switch (alg) {
%(algorithm_cases)s
default:
%(algorithm_code)s{
@ -83,9 +60,6 @@ static int psa_snprint_algorithm(char *buffer, size_t buffer_size,
}
break;
}
if (padding_mode != (psa_algorithm_t) -1) {
append_padding_mode(&buffer, buffer_size, &required_size, padding_mode);
}
buffer[0] = 0;
return required_size;
}
@ -125,10 +99,10 @@ key_type_from_curve_template = '''if (%(tester)s(type)) {
PSA_KEY_TYPE_GET_CURVE(type));
} else '''
algorithm_from_hash_template = '''if (%(tester)s(alg_without_padding)) {
algorithm_from_hash_template = '''if (%(tester)s(alg)) {
append_with_hash(&buffer, buffer_size, &required_size,
"%(builder)s", %(builder_length)s,
PSA_ALG_GET_HASH(alg_without_padding));
PSA_ALG_GET_HASH(alg));
} else '''
bit_test_template = '''\
@ -149,7 +123,6 @@ class MacroCollector:
self.ecc_curves = set()
self.algorithms = set()
self.hash_algorithms = set()
self.block_cipher_padding_modes = set()
self.algorithms_from_hash = {}
self.key_usages = set()
@ -175,11 +148,8 @@ class MacroCollector:
self.key_types_from_curve[name] = name[:13] + 'IS_' + name[13:]
elif name.startswith('PSA_ECC_CURVE_') and not parameter:
self.ecc_curves.add(name)
elif name.startswith('PSA_ALG_BLOCK_CIPHER_PAD_') and not parameter:
self.block_cipher_padding_modes.add(name)
elif name.startswith('PSA_ALG_') and not parameter:
if name in ['PSA_ALG_BLOCK_CIPHER_BASE',
'PSA_ALG_ECDSA_BASE',
if name in ['PSA_ALG_ECDSA_BASE',
'PSA_ALG_RSA_PKCS1V15_SIGN_BASE']:
# Ad hoc skipping of duplicate names for some numerical values
return
@ -250,10 +220,6 @@ class MacroCollector:
return '\n '.join(map(self.make_return_case,
sorted(self.hash_algorithms)))
def make_padding_mode_cases(self):
return '\n '.join(map(self.make_inner_append_case,
sorted(self.block_cipher_padding_modes)))
def make_algorithm_cases(self):
return '\n '.join(map(self.make_append_case,
sorted(self.algorithms)))
@ -279,7 +245,6 @@ class MacroCollector:
data['key_type_cases'] = self.make_key_type_cases()
data['key_type_code'] = self.make_key_type_code()
data['hash_algorithm_cases'] = self.make_hash_algorithm_cases()
data['padding_mode_cases'] = self.make_padding_mode_cases()
data['algorithm_cases'] = self.make_algorithm_cases()
data['algorithm_code'] = self.make_algorithm_code()
data['key_usage_code'] = self.make_key_usage_code()