Botan 3.3.0
Crypto and TLS for C&
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Botan::TLS::Session_Manager_In_Memory Class Reference

#include <tls_session_manager_memory.h>

Inheritance diagram for Botan::TLS::Session_Manager_In_Memory:
Botan::TLS::Session_Manager

Public Member Functions

size_t capacity () const
 
virtual std::optional< std::pair< Session, uint16_t > > choose_from_offered_tickets (const std::vector< PskIdentity > &tickets, std::string_view hash_function, Callbacks &callbacks, const Policy &policy)
 
bool emits_session_tickets () override
 
virtual std::optional< Session_Handleestablish (const Session &session, const std::optional< Session_ID > &id=std::nullopt, bool tls12_no_ticket=false)
 Save a new Session and assign a Session_Handle (TLS Server)
 
virtual std::vector< Session_with_Handlefind (const Server_Information &info, Callbacks &callbacks, const Policy &policy)
 Find all sessions that match a given server info.
 
size_t remove (const Session_Handle &handle) override
 
size_t remove_all () override
 
virtual std::optional< Sessionretrieve (const Session_Handle &handle, Callbacks &callbacks, const Policy &policy)
 Retrieves a specific session given a handle.
 
 Session_Manager_In_Memory (const std::shared_ptr< RandomNumberGenerator > &rng, size_t max_sessions=1000)
 
void store (const Session &session, const Session_Handle &handle) override
 Save a Session under a Session_Handle (TLS Client)
 

Protected Member Functions

std::vector< Session_with_Handlefind_some (const Server_Information &info, size_t max_sessions_hint) override
 Internal retrieval function to find sessions to resume.
 
recursive_mutex_typemutex ()
 
std::optional< Sessionretrieve_one (const Session_Handle &handle) override
 Internal retrieval function for a single session.
 

Protected Attributes

std::shared_ptr< RandomNumberGeneratorm_rng
 

Detailed Description

A thread-safe Session_Manager that stores TLS sessions in memory.

The Session_Handle objects emitted by this manager when establishing a new session (i.e in the TLS server) will never contain a Session_Ticket but only a Session_ID. Storing received sessions (i.e. in the TLS client) under either a Session_ID or a Session_Ticket will however echo them back.

In other words, this manager will support ticket-based resumption in a TLS client but it won't issue tickets on a TLS server.

For applications that implement a TLS client and that do not want to persist sessions to non-volatile memory, this is typically a good default option.

Definition at line 39 of file tls_session_manager_memory.h.

Constructor & Destructor Documentation

◆ Session_Manager_In_Memory()

Botan::TLS::Session_Manager_In_Memory::Session_Manager_In_Memory ( const std::shared_ptr< RandomNumberGenerator > & rng,
size_t max_sessions = 1000 )
Parameters
rnga RNG used for generating session key and for session encryption
max_sessionsa hint on the maximum number of sessions to keep in memory at any one time. (If zero, don't cap)

Definition at line 18 of file tls_session_manager_memory.cpp.

19 :
20 Session_Manager(rng), m_max_sessions(max_sessions) {
21 if(max_sessions > 0) {
22 m_fifo.emplace();
23 }
24}
Session_Manager(const std::shared_ptr< RandomNumberGenerator > &rng)

Member Function Documentation

◆ capacity()

size_t Botan::TLS::Session_Manager_In_Memory::capacity ( ) const
inline

Definition at line 53 of file tls_session_manager_memory.h.

53{ return m_max_sessions; }

Referenced by store().

◆ choose_from_offered_tickets()

std::optional< std::pair< Session, uint16_t > > Botan::TLS::Session_Manager::choose_from_offered_tickets ( const std::vector< PskIdentity > & tickets,
std::string_view hash_function,
Callbacks & callbacks,
const Policy & policy )
virtualinherited

Lets the server application choose a PSK to use for a new TLS connection. Implementers must make sure that the PSK's associated hash function is equal to the passed hash_function.

RFC 8446 4.2.11 The server MUST ensure that it selects a compatible PSK (if any) and cipher suite.

The default implementation simply tries to retrieve all tickets in the order offered by the peer and picks the first that is found and features a matching hash algorithm.

This method is called only by TLS 1.3 servers.

Parameters
ticketsa list of tickets that were offered by the client
hash_functionthe hash algorithm name we are going to use for the to-be-negotiated connection
callbackscallbacks to be used for session policy decisions
policypolicy to be used for session policy decisions
Returns
a std::pair of the Session associated to the choosen PSK and the index of the selected ticket; std::nullopt if no PSK was chosen for usage (will result in a full handshake)
Note
if no PSK is chosen, the server will attempt a regular handshake.

Definition at line 206 of file tls_session_manager.cpp.

210 {
211 // Note that the TLS server currently does not ensure that tickets aren't
212 // reused. As a result, no locking is required on this level.
213
214 for(uint16_t i = 0; const auto& ticket : tickets) {
215 auto session = retrieve(Opaque_Session_Handle(ticket.identity()), callbacks, policy);
216 if(session.has_value() && session->ciphersuite().prf_algo() == hash_function &&
217 session->version().is_tls_13_or_later()) {
218 return std::pair{std::move(session.value()), i};
219 }
220
221 // RFC 8446 4.2.10
222 // For PSKs provisioned via NewSessionTicket, a server MUST validate
223 // that the ticket age for the selected PSK identity [...] is within a
224 // small tolerance of the time since the ticket was issued. If it is
225 // not, the server SHOULD proceed with the handshake but reject 0-RTT,
226 // and SHOULD NOT take any other action that assumes that this
227 // ClientHello is fresh.
228 //
229 // TODO: The ticket-age is currently not checked (as 0-RTT is not
230 // implemented) and we simply take the SHOULD at face value.
231 // Instead we could add a policy check letting the user decide.
232
233 ++i;
234 }
235
236 return std::nullopt;
237}
virtual std::optional< Session > retrieve(const Session_Handle &handle, Callbacks &callbacks, const Policy &policy)
Retrieves a specific session given a handle.
Strong< std::vector< uint8_t >, struct Opaque_Session_Handle_ > Opaque_Session_Handle
holds an opaque session handle as used in TLS 1.3 that could be either a ticket for stateless resumpt...
Definition tls_session.h:39

Referenced by Botan::TLS::PSK::select_offered_psk().

◆ emits_session_tickets()

bool Botan::TLS::Session_Manager_In_Memory::emits_session_tickets ( )
inlineoverridevirtual

Declares whether the given Session_Manager implementation may emit session tickets. Note that this does not mean that the implementation must always emit tickets.

Concrete implementations should declare this, to allow the TLS implementations to act accordingly. E.g. to advertise support for session tickets in their Server Hello.

Returns
true if the Session_Manager produces session tickets

Reimplemented from Botan::TLS::Session_Manager.

Definition at line 55 of file tls_session_manager_memory.h.

55{ return false; }

◆ establish()

std::optional< Session_Handle > Botan::TLS::Session_Manager::establish ( const Session & session,
const std::optional< Session_ID > & id = std::nullopt,
bool tls12_no_ticket = false )
virtualinherited

Save a new Session and assign a Session_Handle (TLS Server)

Save a new session on a best effort basis; the manager may not in fact be able to save the session for whatever reason; this is not an error. Callers cannot assume that calling establish() followed immediately by retrieve() or choose_from_offered_tickets() will result in a successful lookup. In case no session was stored, std::nullopt is returned.

This method is only called on TLS servers.

Note that implementations will silently refrain from sending session tickets to the client when this method returns std::nullopt.

Parameters
sessionto save
idto use (instead of an ID chosen by the manager)
tls12_no_ticketdisable tickets for this establishment (set when TLS 1.2 client does not support them)
Returns
a Session_Handle containing either an ID or a ticket if the session was saved, otherwise std::nullopt

Reimplemented in Botan::TLS::Session_Manager_Noop, Botan::TLS::Session_Manager_Hybrid, and Botan::TLS::Session_Manager_Stateless.

Definition at line 21 of file tls_session_manager.cpp.

23 {
24 // Establishing a session does not require locking at this level as
25 // concurrent TLS instances on a server will create unique sessions.
26
27 // By default, the session manager does not emit session tickets anyway
28 BOTAN_UNUSED(tls12_no_ticket);
29 BOTAN_ASSERT(session.side() == Connection_Side::Server, "Client tried to establish a session");
30
31 Session_Handle handle(id.value_or(m_rng->random_vec<Session_ID>(32)));
32 store(session, handle);
33 return handle;
34}
#define BOTAN_UNUSED
Definition assert.h:118
#define BOTAN_ASSERT(expr, assertion_made)
Definition assert.h:50
virtual void store(const Session &session, const Session_Handle &handle)=0
Save a Session under a Session_Handle (TLS Client)
std::shared_ptr< RandomNumberGenerator > m_rng
Strong< std::vector< uint8_t >, struct Session_ID_ > Session_ID
holds a TLS 1.2 session ID for stateful resumption
Definition tls_session.h:32

References BOTAN_ASSERT, BOTAN_UNUSED, Botan::TLS::Session_Manager::m_rng, Botan::TLS::Server, Botan::TLS::Session_Base::side(), and Botan::TLS::Session_Manager::store().

◆ find()

std::vector< Session_with_Handle > Botan::TLS::Session_Manager::find ( const Server_Information & info,
Callbacks & callbacks,
const Policy & policy )
virtualinherited

Find all sessions that match a given server info.

TLS clients use this to obtain session resumption information for a server they are wishing to handshake with. Typically, session info will have been received in prior connections to that same server and stored using Session_Manager::store().

The default implementation will invoke Session_Manager::find_some() and filter the result against a policy. Most notably an expiry check. Expired sessions will be removed via Session_Manager::remove().

The TLS client implementations will query the session manager exactly once per handshake attempt. If no reuse is desired, the session manager may remove the sessions internally when handing them out to the client. The default implementation adheres to Policy::reuse_session_tickets().

For TLS 1.2 the client implementation will attempt a resumption with the first session in the returned list. For TLS 1.3, it will offer all found sessions to the server.

Applications that wish to implement their own Session_Manager may override the default implementation to add further policy checks. Though, typically implementing Session_Manager::find_some() and relying on the default implementation is enough.

Parameters
infothe info about the server we want to handshake with
callbackscallbacks to be used for session policy decisions
policypolicy to be used for session policy decisions
Returns
a list of usable sessions that might be empty if no such session exists or passed the policy validation

Reimplemented in Botan::TLS::Session_Manager_Hybrid.

Definition at line 161 of file tls_session_manager.cpp.

163 {
164 auto allow_reusing_tickets = policy.reuse_session_tickets();
165
166 // Session_Manager::find() must be an atomic getter if ticket reuse is not
167 // allowed. I.e. each ticket handed to concurrently requesting threads must
168 // be unique. In that case we must hold a lock while retrieving a ticket.
169 // Otherwise, no locking is required on this level.
170 std::optional<lock_guard_type<recursive_mutex_type>> lk;
171 if(!allow_reusing_tickets) {
172 lk.emplace(mutex());
173 }
174
175 auto sessions_and_handles = find_and_filter(info, callbacks, policy);
176
177 // std::vector::resize() cannot be used as the vector's members aren't
178 // default constructible.
179 const auto session_limit = policy.maximum_session_tickets_per_client_hello();
180 while(session_limit > 0 && sessions_and_handles.size() > session_limit) {
181 sessions_and_handles.pop_back();
182 }
183
184 // RFC 8446 Appendix C.4
185 // Clients SHOULD NOT reuse a ticket for multiple connections. Reuse of
186 // a ticket allows passive observers to correlate different connections.
187 //
188 // When reuse of session tickets is not allowed, remove all tickets to be
189 // returned from the implementation's internal storage.
190 if(!allow_reusing_tickets) {
191 // The lock must be held here, otherwise we cannot guarantee the
192 // transactional retrieval of tickets to concurrently requesting clients.
193 BOTAN_ASSERT_NOMSG(lk.has_value());
194 for(const auto& [session, handle] : sessions_and_handles) {
195 if(!session.version().is_pre_tls_13() || !handle.is_id()) {
196 remove(handle);
197 }
198 }
199 }
200
201 return sessions_and_handles;
202}
#define BOTAN_ASSERT_NOMSG(expr)
Definition assert.h:59
virtual size_t remove(const Session_Handle &handle)=0
recursive_mutex_type & mutex()

References BOTAN_ASSERT_NOMSG, Botan::TLS::Policy::maximum_session_tickets_per_client_hello(), and Botan::TLS::Policy::reuse_session_tickets().

◆ find_some()

std::vector< Session_with_Handle > Botan::TLS::Session_Manager_In_Memory::find_some ( const Server_Information & info,
size_t max_sessions_hint )
overrideprotectedvirtual

Internal retrieval function to find sessions to resume.

Try to find saved sessions using info about the server we're planning to connect to. It should return a list of sessions in preference order of the session manager.

Applications that wish to implement their own Session_Manager will have to provide an implementation for it.

Note that the TLS client implementations do not perform any checks on the validity of the session for a given info. Particularly, it is the Session_Manager's responsibility to ensure the restrictions posed in RFC 8446 4.6.1 regarding server certificate validity for the given info.

This is called for TLS clients only.

Parameters
infothe information about the server
max_sessions_hinta non-binding guideline for an upper bound of sessions to return from this method (will be at least 1 but potentially more)
Returns
the found sessions along with their handles (containing either a session ID or a ticket)

Implements Botan::TLS::Session_Manager.

Definition at line 63 of file tls_session_manager_memory.cpp.

64 {
65 BOTAN_UNUSED(max_sessions_hint);
66
67 lock_guard_type<recursive_mutex_type> lk(mutex());
68
69 std::vector<Session_with_Handle> found_sessions;
70 // TODO: std::copy_if?
71 for(const auto& [_, session_and_handle] : m_sessions) {
72 if(session_and_handle.session.server_info() == info) {
73 found_sessions.emplace_back(session_and_handle);
74 }
75 }
76
77 return found_sessions;
78}

References BOTAN_UNUSED, and Botan::TLS::Session_Manager::mutex().

◆ mutex()

recursive_mutex_type & Botan::TLS::Session_Manager::mutex ( )
inlineprotectedinherited

◆ remove()

size_t Botan::TLS::Session_Manager_In_Memory::remove ( const Session_Handle & handle)
overridevirtual

Remove a specific session from the cache, if it exists. The handle might contain either a session ID or a ticket.

Parameters
handlea Session_Handle of the session to be removed
Returns
the number of sessions that were removed

Implements Botan::TLS::Session_Manager.

Definition at line 80 of file tls_session_manager_memory.cpp.

80 {
81 lock_guard_type<recursive_mutex_type> lk(mutex());
82 return remove_internal(handle);
83}

References Botan::TLS::Session_Manager::mutex().

◆ remove_all()

size_t Botan::TLS::Session_Manager_In_Memory::remove_all ( )
overridevirtual

Remove all sessions from the cache

Returns
the number of sessions that were removed

Implements Botan::TLS::Session_Manager.

Definition at line 126 of file tls_session_manager_memory.cpp.

126 {
127 lock_guard_type<recursive_mutex_type> lk(mutex());
128
129 const auto sessions = m_sessions.size();
130 m_sessions.clear();
131 if(m_fifo.has_value()) {
132 m_fifo->clear();
133 }
134
135 return sessions;
136}

References Botan::TLS::Session_Manager::mutex().

◆ retrieve()

std::optional< Session > Botan::TLS::Session_Manager::retrieve ( const Session_Handle & handle,
Callbacks & callbacks,
const Policy & policy )
virtualinherited

Retrieves a specific session given a handle.

This is typically used by TLS servers to obtain resumption information for a previous call to Session_Manager::establish() when a client requested resumption using the handle.

Even if the session is found successfully, it is returned only if it passes policy validations. Most notably an expiry check. If the expiry check fails, the default implementation calls Session_Manager::remove() for the provided handle.

Applications that wish to implement their own Session_Manager may override the default implementation to add further policy checks. Though, typically implementing Session_Manager::retrieve_one() and relying on the default implementation is enough.

Parameters
handlethe Session_Handle to be retrieved
callbackscallbacks to be used for session policy decisions
policypolicy to be used for session policy decisions
Returns
the obtained session or std::nullopt if no session was found or the policy checks failed

Reimplemented in Botan::TLS::Session_Manager_Hybrid.

Definition at line 36 of file tls_session_manager.cpp.

38 {
39 // Retrieving a session for a given handle does not require locking on this
40 // level. Concurrent threads might handle the removal of an expired ticket
41 // more than once, but removing an already removed ticket is a harmless NOOP.
42
43 auto session = retrieve_one(handle);
44 if(!session.has_value()) {
45 return std::nullopt;
46 }
47
48 // A value of '0' means: No policy restrictions.
49 const std::chrono::seconds policy_lifetime =
50 (policy.session_ticket_lifetime().count() > 0) ? policy.session_ticket_lifetime() : std::chrono::seconds::max();
51
52 // RFC 5077 3.3 -- "Old Session Tickets"
53 // A server MAY treat a ticket as valid for a shorter or longer period of
54 // time than what is stated in the ticket_lifetime_hint.
55 //
56 // RFC 5246 F.1.4 -- TLS 1.2
57 // If either party suspects that the session may have been compromised, or
58 // that certificates may have expired or been revoked, it should force a
59 // full handshake. An upper limit of 24 hours is suggested for session ID
60 // lifetimes.
61 //
62 // RFC 8446 4.6.1 -- TLS 1.3
63 // A server MAY treat a ticket as valid for a shorter period of time than
64 // what is stated in the ticket_lifetime.
65 //
66 // Note: This disregards what is stored in the session (e.g. "lifetime_hint")
67 // and only takes the local policy into account. The lifetime stored in
68 // the sessions was taken from the same policy anyways and changes by
69 // the application should have an immediate effect.
70 const auto ticket_age =
71 std::chrono::duration_cast<std::chrono::seconds>(callbacks.tls_current_timestamp() - session->start_time());
72 const bool expired = ticket_age > policy_lifetime;
73
74 if(expired) {
75 remove(handle);
76 return std::nullopt;
77 } else {
78 return session;
79 }
80}
virtual std::optional< Session > retrieve_one(const Session_Handle &handle)=0
Internal retrieval function for a single session.

References Botan::TLS::Session_Manager::remove(), Botan::TLS::Session_Manager::retrieve_one(), Botan::TLS::Policy::session_ticket_lifetime(), and Botan::TLS::Callbacks::tls_current_timestamp().

◆ retrieve_one()

std::optional< Session > Botan::TLS::Session_Manager_In_Memory::retrieve_one ( const Session_Handle & handle)
overrideprotectedvirtual

Internal retrieval function for a single session.

Try to obtain a Session from a Session_Handle that contains either a session ID or a session ticket. This method should not apply any policy decision (such as ticket expiry) but simply be a storage interface.

Applications that wish to implement their own Session_Manager will have to provide an implementation for it.

This method is called only by servers.

Parameters
handlea Session_Handle containing either an ID or a ticket
Returns
the obtained session or std::nullopt if none can be obtained

Implements Botan::TLS::Session_Manager.

Definition at line 50 of file tls_session_manager_memory.cpp.

50 {
51 lock_guard_type<recursive_mutex_type> lk(mutex());
52
53 if(auto id = handle.id()) {
54 const auto session = m_sessions.find(id.value());
55 if(session != m_sessions.end()) {
56 return session->second.session;
57 }
58 }
59
60 return std::nullopt;
61}

References Botan::TLS::Session_Handle::id(), and Botan::TLS::Session_Manager::mutex().

◆ store()

void Botan::TLS::Session_Manager_In_Memory::store ( const Session & session,
const Session_Handle & handle )
overridevirtual

Save a Session under a Session_Handle (TLS Client)

Save a session on a best effort basis; the manager may not in fact be able to save the session for whatever reason; this is not an error. Callers cannot assume that calling store() followed immediately by find() will result in a successful lookup.

In contrast to establish(), this stores sessions that were created by the server along with a Session_Handle also coined by the server.

This method is only called on TLS clients.

Parameters
sessionto save
handlea Session_Handle on which this session shoud by stored

Implements Botan::TLS::Session_Manager.

Definition at line 26 of file tls_session_manager_memory.cpp.

26 {
27 // TODO: C++20 allows CTAD for template aliases (read: lock_guard_type), so
28 // technically we should be able to omit the explicit mutex type.
29 // Unfortuately clang does not agree, yet.
30 lock_guard_type<recursive_mutex_type> lk(mutex());
31
32 if(m_fifo.has_value()) {
33 while(m_sessions.size() >= capacity()) {
34 BOTAN_ASSERT_NOMSG(m_sessions.size() <= m_fifo->size());
35 m_sessions.erase(m_fifo->front());
36 m_fifo->pop_front();
37 }
38 }
39
40 // Generate a random session ID if the peer did not provide one. Note that
41 // this ID is just for internal use and won't be returned on ::find().
42 auto id = handle.id().value_or(m_rng->random_vec<Session_ID>(32));
43 m_sessions.emplace(id, Session_with_Handle{session, handle});
44
45 if(m_fifo.has_value()) {
46 m_fifo->emplace_back(std::move(id));
47 }
48}

References BOTAN_ASSERT_NOMSG, capacity(), Botan::TLS::Session_Handle::id(), Botan::TLS::Session_Manager::m_rng, and Botan::TLS::Session_Manager::mutex().

Member Data Documentation

◆ m_rng

std::shared_ptr<RandomNumberGenerator> Botan::TLS::Session_Manager::m_rng
protectedinherited

The documentation for this class was generated from the following files: