WIP: RFC: Create type SecureString

base/exports.jl

@@ -74,6 +74,7 @@ export
     RoundNearestTiesUp,
     RoundToZero,
     RoundUp,
+    SecureString,
     Set,
     Some,
     StepRange,
@@ -592,6 +593,7 @@ export
     rpad,
     rsplit,
     rstrip,
+    shred!,
     split,
     string,
     strip,

base/strings/secure.jl

@@ -0,0 +1,82 @@
+"""
+    SecureString(string::AbstractString)
+
+A string where the contents will be securely wiped when garbage collected. However, it is
+considered best practise to wipe the string using `shred!(::SecureString)` as soon as the
+secure data is no longer required. Note that when the parameter is of type `Vector{UInt8}`
+then the memory of the passed in parameter will also be securely wiped.
+
+# Examples
+```jldoctest
+julia> str = "abc"::String
+"abc"
+
+julia> s = SecureString(str)
+"abc"
+
+julia> shred!(s)
+"\0\0\0"
+
+julia> str
+"abc"
+```
+"""
+mutable struct SecureString <: AbstractString
+    data::Vector{UInt8}
+
+    function SecureString(data::Vector{UInt8})
+        s = new(data)
+        finalizer(final_shred!, s)
+        return s
+    end
+end
+
+SecureString(str::String) = SecureString(copy(unsafe_wrap(Vector{UInt8}, str)))
+SecureString(str::Union{AbstractString,CodeUnits}) = SecureString(String(str))
+
+show(io::IO, s::SecureString) = print(io, "SecureString(\"*****\")")
+write(io::IO, s::SecureString) = write(io, s.data)
+
+function print(io::IO, s::SecureString)
+    write(io, s.data)
+    nothing
+end
+
+String(s::SecureString) = String(copy(s.data))
+
+iterate(s::SecureString, i::Integer=firstindex(s)) = iterate(String(s), i)
+ncodeunits(s::SecureString) = Core.sizeof(s.data)
+codeunit(s::SecureString) = UInt8
+codeunit(s::SecureString, i::Integer) = s.data[i]
+
+isvalid(s::SecureString, i::Int) = isvalid(String(s), i)
+
+==(a::SecureString, b::SecureString) = a.data == b.data
+==(a::String, b::SecureString) = unsafe_wrap(Vector{UInt8}, a) == b.data
+==(a::AbstractString, b::SecureString) = String(a) == b
+==(a::SecureString, b::AbstractString) = b == a
+
+function final_shred!(s::SecureString)
+    if !isshredded(s)
+        # TODO: Printing SecureString data is temporary while I locate issues in tests
+        # Note: `@warn` won't work here
+        println("SecureString \"$s\" not explicitly shredded")
+        shred!(s)
+    end
+end
+
+function shred!(s::SecureString)
+    securezero!(s.data)
+    return s
+end
+
+isshredded(s::SecureString) = sum(s.data) == 0
+
+function shred!(f::Function, x)
+    try
+        f(x)
+    finally
+        shred!(x)
+    end
+    x
+end

base/strings/strings.jl

@@ -9,3 +9,4 @@ import .Unicode: textwidth, islowercase, isuppercase, isletter, isdigit, isnumer
 
 include("strings/util.jl")
 include("strings/io.jl")
+include("strings/secure.jl")

base/util.jl

@@ -447,7 +447,7 @@ securezero!(s::String) = unsafe_securezero!(pointer(s), sizeof(s))
 unsafe_securezero!(p::Ptr{Cvoid}, len::Integer=1) = Ptr{Cvoid}(unsafe_securezero!(Ptr{UInt8}(p), len))
 
 if Sys.iswindows()
-function getpass(prompt::AbstractString)
+function getpass(prompt::AbstractString)::SecureString
     print(prompt)
     flush(stdout)
     p = Vector{UInt8}(undef, 128) # mimic Unix getpass in ignoring more than 128-char passwords
@@ -475,11 +475,13 @@ function getpass(prompt::AbstractString)
     return ""
 end
 else
-getpass(prompt::AbstractString) = unsafe_string(ccall(:getpass, Cstring, (Cstring,), prompt))
+function getpass(prompt::AbstractString)::SecureString
+    unsafe_string(ccall(:getpass, Cstring, (Cstring,), prompt))
+end
 end
 
 """
-    prompt(message; default="", password=false) -> Union{String, Nothing}
+    prompt(message; default="", password=false) -> Union{AbstractString, Nothing}
 
 Displays the `message` then waits for user input. Input is terminated when a newline (\\n)
 is encountered or EOF (^D) character is entered on a blank line. If a `default` is provided
@@ -583,7 +585,7 @@ if Sys.iswindows()
         # Done.
         passbuf_ = passbuf[1:passlen[]-1]
         result = (String(transcode(UInt8, usernamebuf[1:usernamelen[]-1])),
-                  String(transcode(UInt8, passbuf_)))
+                  SecureString(transcode(UInt8, passbuf_)))
         securezero!(passbuf_)
         securezero!(passbuf)
 

stdlib/LibGit2/src/callbacks.jl

@@ -190,7 +190,7 @@ function authenticate_userpass(libgit2credptr::Ptr{Ptr{Cvoid}}, p::CredentialPay
         # Use `deepcopy` to ensure zeroing the `git_cred` doesn't also zero the `cred`s copy
         cred.user = deepcopy(something(git_cred.username, ""))
         cred.pass = deepcopy(something(git_cred.password, ""))
-        securezero!(git_cred)
+        shred!(git_cred)
         revised = true
 
         p.use_git_helpers = false

stdlib/LibGit2/src/gitcredential.jl

@@ -7,11 +7,11 @@ Git credential information used in communication with git credential helpers. Th
 named using the [input/output key specification](https://git-scm.com/docs/git-credential#IOFMT).
 """
 mutable struct GitCredential
-    protocol::Union{String, Nothing}
-    host::Union{String, Nothing}
-    path::Union{String, Nothing}
-    username::Union{String, Nothing}
-    password::Union{String, Nothing}
+    protocol::Union{SecureString, Nothing}
+    host::Union{SecureString, Nothing}
+    path::Union{SecureString, Nothing}
+    username::Union{SecureString, Nothing}
+    password::Union{SecureString, Nothing}
     use_http_path::Bool
 
     function GitCredential(
@@ -20,9 +20,7 @@ mutable struct GitCredential
             path::Union{AbstractString, Nothing}=nothing,
             username::Union{AbstractString, Nothing}=nothing,
             password::Union{AbstractString, Nothing}=nothing)
-        c = new(protocol, host, path, username, password, true)
-        finalizer(securezero!, c)
-        return c
+        new(protocol, host, path, username, password, true)
     end
 end
 
@@ -32,17 +30,17 @@ end
 
 function GitCredential(cred::UserPasswordCredential, url::AbstractString)
     git_cred = parse(GitCredential, url)
-    git_cred.username = deepcopy(cred.user)
-    git_cred.password = deepcopy(cred.pass)
+    git_cred.username = SecureString(cred.user)
+    git_cred.password = SecureString(cred.pass)
     return git_cred
 end
 
-function securezero!(cred::GitCredential)
-    cred.protocol !== nothing && securezero!(cred.protocol)
-    cred.host !== nothing && securezero!(cred.host)
-    cred.path !== nothing && securezero!(cred.path)
-    cred.username !== nothing && securezero!(cred.username)
-    cred.password !== nothing && securezero!(cred.password)
+function shred!(cred::GitCredential)
+    cred.protocol !== nothing && shred!(cred.protocol)
+    cred.host !== nothing && shred!(cred.host)
+    cred.path !== nothing && shred!(cred.path)
+    cred.username !== nothing && shred!(cred.username)
+    cred.password !== nothing && shred!(cred.password)
     return cred
 end
 
@@ -90,12 +88,11 @@ function Base.parse(::Type{GitCredential}, url::AbstractString)
 end
 
 function Base.copy!(a::GitCredential, b::GitCredential)
-    # Note: deepcopy calls avoid issues with securezero!
-    a.protocol = deepcopy(b.protocol)
-    a.host = deepcopy(b.host)
-    a.path = deepcopy(b.path)
-    a.username = deepcopy(b.username)
-    a.password = deepcopy(b.password)
+    a.protocol = b.protocol
+    a.host = b.host
+    a.path = b.path
+    a.username = b.username
+    a.password = b.password
     return a
 end
 
@@ -116,9 +113,12 @@ function Base.read!(io::IO, cred::GitCredential)
         if key == "url"
             # Any components which are missing from the URL will be set to empty
             # https://git-scm.com/docs/git-credential#git-credential-codeurlcode
+            shred!(cred)
             copy!(cred, parse(GitCredential, value))
         else
-            Base.setproperty!(cred, Symbol(key), String(value))
+            field = getproperty(cred, Symbol(key))
+            field !== nothing && shred!(field)
+            setproperty!(cred, Symbol(key), String(value))
         end
     end
 
@@ -283,7 +283,7 @@ function approve(cfg::GitConfig, cred::UserPasswordCredential, url::AbstractStri
         approve(helper, git_cred)
     end
 
-    securezero!(git_cred)
+    shred!(git_cred)
     nothing
 end
 
@@ -295,6 +295,6 @@ function reject(cfg::GitConfig, cred::UserPasswordCredential, url::AbstractStrin
         reject(helper, git_cred)
     end
 
-    securezero!(git_cred)
+    shred!(git_cred)
     nothing
 end

stdlib/LibGit2/src/types.jl

@@ -1172,7 +1172,7 @@ function objtype(obj_type::Consts.OBJECT)
     end
 end
 
-import Base.securezero!
+import Base.shred!
 
 abstract type AbstractCredential end
 
@@ -1185,12 +1185,10 @@ isfilled(::AbstractCredential)
 
 "Credential that support only `user` and `password` parameters"
 mutable struct UserPasswordCredential <: AbstractCredential
-    user::String
-    pass::String
+    user::SecureString
+    pass::SecureString
     function UserPasswordCredential(user::AbstractString="", pass::AbstractString="")
-        c = new(user, pass)
-        finalizer(securezero!, c)
-        return c
+        new(user, pass)
     end
 
     # Deprecated constructors
@@ -1204,9 +1202,9 @@ mutable struct UserPasswordCredential <: AbstractCredential
     UserPasswordCredential(prompt_if_incorrect::Bool) = UserPasswordCredential("","",prompt_if_incorrect)
 end
 
-function securezero!(cred::UserPasswordCredential)
-    securezero!(cred.user)
-    securezero!(cred.pass)
+function shred!(cred::UserPasswordCredential)
+    shred!(cred.user)
+    shred!(cred.pass)
     return cred
 end
 
@@ -1220,15 +1218,13 @@ end
 
 "SSH credential type"
 mutable struct SSHCredential <: AbstractCredential
-    user::String
-    pass::String
-    prvkey::String
-    pubkey::String
+    user::SecureString
+    pass::SecureString
+    prvkey::SecureString
+    pubkey::SecureString
     function SSHCredential(user::AbstractString="", pass::AbstractString="",
-                            prvkey::AbstractString="", pubkey::AbstractString="")
-        c = new(user, pass, prvkey, pubkey)
-        finalizer(securezero!, c)
-        return c
+                           prvkey::AbstractString="", pubkey::AbstractString="")
+        new(user, pass, prvkey, pubkey)
     end
 
     # Deprecated constructors
@@ -1243,11 +1239,11 @@ mutable struct SSHCredential <: AbstractCredential
     SSHCredential(prompt_if_incorrect::Bool) = SSHCredential("","","","",prompt_if_incorrect)
 end
 
-function securezero!(cred::SSHCredential)
-    securezero!(cred.user)
-    securezero!(cred.pass)
-    securezero!(cred.prvkey)
-    securezero!(cred.pubkey)
+function shred!(cred::SSHCredential)
+    shred!(cred.user)
+    shred!(cred.pass)
+    shred!(cred.prvkey)
+    shred!(cred.pubkey)
     return cred
 end
 
@@ -1270,8 +1266,8 @@ Base.haskey(cache::CachedCredentials, cred_id) = Base.haskey(cache.cred, cred_id
 Base.getindex(cache::CachedCredentials, cred_id) = Base.getindex(cache.cred, cred_id)
 Base.get!(cache::CachedCredentials, cred_id, default) = Base.get!(cache.cred, cred_id, default)
 
-function securezero!(p::CachedCredentials)
-    foreach(securezero!, values(p.cred))
+function shred!(p::CachedCredentials)
+    foreach(shred!, values(p.cred))
     return p
 end
 
@@ -1385,7 +1381,7 @@ function approve(p::CredentialPayload; shred::Bool=true)
         approve(p.config, cred, p.url)
     end
 
-    shred && securezero!(cred)
+    shred && shred!(cred)
     nothing
 end
 
@@ -1410,7 +1406,7 @@ function reject(p::CredentialPayload; shred::Bool=true)
         reject(p.config, cred, p.url)
     end
 
-    shred && securezero!(cred)
+    shred && shred!(cred)
     nothing
 end